Alright. So the point of this thread is to provide a vehicle for me to establish a universal baseline, appropriate to the codices, for equipment to exist side by side. It'll follow a very simple series of baseline conversion formulae.

First off, Armour Saves.

I think we can pretty reasonably stick to the rough baseline Fantasy Flight Games has already established.

A 6+ Armour Save = 2 AP.
A 5+ Armour Save = 4 AP
A 4+ Armour Save = 6 AP
A 3+ Armour Save = 8 AP
A 2+ Armour Save would equal 14 if Terminator Armour and Mega armour are any indicator, but I think this leap is perhaps too great a jump. If we continue to follow the arithmetic progression, then a 2+ armour save should in fact be equivalent to 10AP.

Invulnerable Saves will probably best translate as a Field Save.

6++ = 20%
5++ = 30%
4++ = 40%
3++ = 50%

Range;

24" ~ 100m
12" ~ 30m
18" ~ 60m
48" ~ 200m

Using a Lasgun to estimate a conversion formula for weapon strength.

Lasgun = S3, AP/-

S3 = 1d10 + 3

Therefore a reasonable approx. conversion, according to this logic, Strength value of the gun = raw damage addition to d10 value. Pen can scale according to the weapon, therefore an AP2 weapon should negate 10 armour. AP3 hotshot pens 8 armour, and so on and so forth.

Only thing I think I need to consider now is the special properties of the weapon, such as Tearing. Those would probably be sufficient to carry over from official works.

Alright, I think I've captured most things here, and can begin producing the Closer To Codex armoury project from this baseline, but before I do I'm going to give you chaps to weigh in on my reasoning and see if you agree with the maths I've done here.

I disagree with the percentages for the invuln saves. While the initial starting point seems good, the intervals should be 15% rather than 10% like so:

6++: 20%

5++: 35%

4++: 50%

3++: 65%

Not only does this get the middle three percentages close to or exactly the chance it'd have of suceeding on tabletop, but also I recall a 5++ field or two that has a rating of 35 in the roleplaying game--which I am currently too lazy to look up given that it's almost time to go to bed and my computer has been crashing on me quite a bit.