As to the specific character himself, he has Unnatural Strength +3, and Unnatural Toughness +3 (among other things), and these things are part of his genetics (there was a bit of heresy involved, a bunch of rampaging horse lords who looked a lot like Conan, and a bit of character/npc love-making that lead to him).

These traits seem especially strong for a starting character, and I figure an xp handicap should be levied, I'm just not sure what.

Well, in regards to Unnatural Strength, go look at the Augmetics section of the book. Muscle replacement for Unnatural Strength exists, and the Availability on it should give you a rough 'this is how much it is worth.' From there, just figure out a rough 'experience for Availability' model to go with. Then, bust it up a bit for Toughness because that is generally a more applicable/important stat (as at that point your enemies will need Felling weapons or he'll just take 3 damage off on top of his Toughness bonus, which I would expect to be no less than 40).

I honestly wouldn't give him more than 2 in either, by the way. That's surpassing Space Marine physicality.

I'm not getting into whether or not applying a cost to Unnatural Attributes and making them available is a good idea; that's something that'd be table-specific. I wouldn't just let people buy them, but perhaps as a very high-tier reward for a job well done.

Well, SMs have Unnatural +4 to both strength and toughness (as of BC and DH2), so he certainly wouldn't surpass them, especially without power armour, but that he comes close is scary enough. Then again, regular humans and Chaos Space Marines adventure alongside each other in Black Crusade, and I'm told the balance isn't that off between them.

It was probably a foolish endeavor however to try to appraise anything in the traits section really, especially given that so many variables are at play, but once posted....

As to actually buying traits, especially unnaturals, that hasn't really been an issue that has ever come up at our table, though with the Mutant background, it certainly opens up the possibility with homebrew rules.

Actually it is less, as the stats from Power Armor are included in their stat profile. So yeah, he'd probably be surpassing a Space Marine in Strength, which shouldn't be a thing in my mind without mutation or heresy.

Space Marine Unnat Stats are not from their Power Armor, its from their implanted/grown organs. With Power Armor included a Marine has a Strength Bonus of between 10 and 12 base.

I didn't say they all came from Power Armor, but some of it did.

Read the note on page 297 (Deathwatch stat block). **All characteristic modifiers from power armor included in profile.

Since a Space Marine has 4 Unnatural Strength in their stat-block, it means they have to have an Unnatural Strength of less than 4, because even weak Power Armors for mundanes give Unnatural Strength 1. I'd assume Astartes level armor gives 2.

Actually, Astartes Power Armour does not grant Unnatural Strength. It's a flat +20 to strength. So +4 Unnatural Strength is the Space Marine norm.

It's pretty **** hard to surpass a Space Marine's statline as a normal human, not counting techpriests, who can slap on so many augmetics they can win the augmented arms race.

As for your xp handicap, I normally wouldn't include exp costs for something like this. Most of the time they should probably come with weaknesses or a downside, whether that be the use of proscribed technology or a mutation which could get them into trouble if spotted. Augmetics lead to a weakness to haywire weapons and a hostile Techpriest with noospheric access might be able to mess you up. Strength and Toughness +3 seems abit much for an unaugmented human though, even Ogryn really only have Strength and Toughness +2, and they're hulking great brutes who can mess you up any day and they have the downside of being as smart as a sack with a brick in.

It used to give +20 until our wise overlords decided that Power Armor should only give Unnatural Strength. Now Space Marines need to content themselves with being just barely stronger than regular-ass guys even in their massive armored suits.

Huh, I hadn't noticed. I've still been running it the old way. in the case of the Astartes in the Dark Heresy reinforcements however, I believe the power armour is changing their base strength score, it explains the gulf between their strength and toughness scores.

It's pretty **** hard to surpass a Space Marine's statline as a normal human, not counting techpriests, who can slap on so many augmetics they can win the augmented arms race.

As for your xp handicap, I normally wouldn't include exp costs for something like this. Most of the time they should probably come with weaknesses or a downside, whether that be the use of proscribed technology or a mutation which could get them into trouble if spotted. Augmetics lead to a weakness to haywire weapons and a hostile Techpriest with noospheric access might be able to mess you up. Strength and Toughness +3 seems abit much for an unaugmented human though, even Ogryn really only have Strength and Toughness +2, and they're hulking great brutes who can mess you up any day and they have the downside of being as smart as a sack with a brick in.

The GM did give him a few handicaps, which are the same ones he included for his people when they were part of his campaign, though they don't really balance out his bonuses (hence the xp penalty idea). He starts with 10 corruption and -10 Willpower, and per story, he is on the radar of both Tzeench and Slaanesh (as the genetic engineering done to his people was done by cultists devoted to both). If he knocks up anyone, he has a certain chance of passing on his altered genes, with a 10% of fathering a wriggling, tentacled abomination.

As to the +3, his ancestors originally came out of the older system, as they possessed Unnatural Strength and Toughness ×2 rather than +. Given most had a base strength and toughness of 30 (the elites had 40), they were hitting/soaking damage with a bonus of 6, which is where the +3 came from.

Hmmmm.... I'll need to look through the books some more, and discuss it with the GM, as he's the one who built the special bonuses in his genetics. However, given Best Craftsmanship Synth-Muscle grants Unnatural Strength +4 to a regular human (and is legal per game rules), we should be able to work something out, though I'm thinking he may be better off as a background NPC or a latecomer to the party, only joining after they've advanced a good bit.