Moose Biscuits
It would be extreamly painful...
In no particular order...
All High-end/Exotic
Striker's
Reclaimer
Tactician
...that's just a starting point as there are many directions you can go from there regarding preferences (DPS, Tank, Healer, etc). I tend to run most of my Gear Set builds with a Barret's chest (Exotic) and Specialized backpack (High-end). Sometimes I'll use a Sturdy holster (High-end) instead of the Barret's chest. If running a All High-end/Exotic build you really want a Barret's chest and Skull gloves (Exotic).
The D3-FNC set might be worthwhile if you spec into Electronics/Skill Power.
Interesting. I usually just discard any yellow gear I find, in my mind it's inferior to gear set items, but if that's wrong I'll keep an eye out.
I have been trying for Barrett's chest piece though, running Lexington on challenging. At the very least that mission isn't too much of a challenge. If you're doing it with good players it's pretty fun; it's hilarious to watch LaRae walk out the doors and immediately get melted by a barrage of fire turrets, airburst seeker mines and gunfire.