Stock bucking is good but if you want better either get SystemA, Guarder Black, or Prometheus Purple. I'm sure companies like Modify and Madbull make good stuff too but those are the ones I've used.
As far as being disadvantaged; I use .28g BB's in my rifle and I shoot ~395 FPS on .20's so a little under 335 FPS using the .28's. I don't feel I'm at a terrible disadvantage but I do like the increased accuracy of the heavier BB. For the longest time I was using .25g BB's and thought those were great as well and a ~40 FPS drop isn't terrible and you have to keep in mind that paintballers outdoor only play at 330 FPS (because of larger mass of the paintball and safety and such). Either way though .25 or .28, you're not at a disadvantage and most players who know what they're doing will use at least .25 anyways.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE