Some powers like Smite say they use modifiers from ranged attacks for the focus power test. Does this mean you use all of the range modifiers, including long and extreme range? Does this mean Smite with a PR of 5 for a 50m range can actually be used out to 200m with a penalty to the hit roll? If you had the Marksman talent would this negate the penalties? I can see arguments either way. What do you think?

It gets a little confusing, so let me help you out.

Range and Line of Sight: Unless noted in its description, a Psychic Power that directly targets an individual or thing requires a psyker to have line of sight towards (or otherwise be "aware" of) the target. The target must also be within the power's stated range.

Smite: [Range of 10m x PR] : ...However, his Focus Power Test is modified as if he was making a ranged attack (using bonuses and penalties for range, lighting, enemy talents, etc.).

So under Smite's description, you could use the example of a PR 5 Smite of attacking up to 200m away with a -30 penalty, technically. Personally, I just rule Smite has a maximum range of 10m x PR. Saves me a lot of headache and grief.

The Marksman Talent is only for Ballistic Skill Tests. It does not affect Focus Power Tests which is what's required to cast Smite.