Frankly, if I've got a sniper rifle with a decent range, Far shot, and a scope, I'm pretty set. As a rule of thumb, take the following feats:
Double Tap, to do an extra die of damage
Heroic Surge, to get an extra shot
Use the following classes:
Strong Hero (for the BAB progresion), even if your highest score is Dex
Soldier (for the Weapon Focus and Specialization, Tactical Aid, Improved Critical, and automatic Critical Confirmation)
Right there, a 13th level character can fire a sniper rifle and get:
A +1 to hit from Weapon Focus
A +1 (at least) competence bonus from using Tactical Aid
A +4 on damage.
A threat range of 19-20, automatically confirmed.
Now, on TOP of that, you get your Intel guy to work with you. Get a Smart guy with some Occupational ranks in Hide and Move Silently. He gets you into position and tells you the best time to get off your shot based on the target's personal habits, which routes the guy takes, when he stops to talk to folks, etc. The end result of this is that your assistant uses the Plan Talent of the Smart Hero, which can give you a Circumstance bonus on your attacks. Unfortunately, he can't use Aid Another, since that's only for melee, but he CAN give you the world's best plan, which equates to up to a +3 circumstance bonus to hit, which stacks with the (Int bonus) bonus that you got from Tactical aid. Let's say that he's darned good at what he does, and you've got a high intelligence -- after all, they wanted you to be the best sniper, right? +3 from his advice, +3 from your tactical aid. Along with Weapon Focus, you're looking at a +7 to hit. At this point, heck yes, double-tap, and then use your heroic surge and do a double-tap again! Two shots that have an automatically successful crit range of 19-20, do +4 damage anyway, and do an extra die of damage? Based on the average sniper rifle, which does 2d10?
+5 to hit (after double-tapping on each attack), damage of 3d10 + 4, 19-20/x2 (auto).
Sounds like a pretty decent sniper to me.
-Tacky
Edit: Duh, me. Dead Aim, too -- for an extra +2 to hit on top of all that.
Edit 2: Heck, if you wanted to be really goofy, you could have ANOTHER buddy lurking over your shoulder murmuring, "That's right, who da man? YOU da man. You gonna shoot him good, buddy. You gonna shoot him, you gonna shoot him. Who's gonna shoot him? You are. Darn right. A-hoo-yeah!" (Greater Inspiration from the Charismatic Hero, which gives you a +3 morale bonus to attacks and damage.) On the other hand, while I can see a sniper and an Intel guy, I have trouble with imagining the team cheerleader. But if you played it as the Charismatic commander telling him, "Go for it, Hawkeye. I know you can do it," and then music swells as our sniper suddenly realizes that the power to blow the heads off bad guys was within him all along, and he nods, purses his lips, and goes to work... maybe then it'd work.
PPPS: Also, on a one-shot deal like a sniping shot, I'd sure as heck use an action point.
PPPPS: Burst Fire. Why the heck not? You've got all these bonuses. A whole mess of slugs at a whole mess of bonuses, doing a whole mess of damage.
MAN, guns are nasty.
-Tacky, again.