From my experience in CBT, Snipers wielding the 2Handed Sniper Rifle does more burst damage (front-loaded) at the cost of slightly less efficient energy usage. The Gunslinger DW Blaster Pistols with slightly better sustained damage (back-loaded) and energy efficiency.
Yes, they are mirrored classes. But when you factor in DW and OH Miss/Damage changes compared to a single 2H Sniper Rifle, the Sniper Rifle will hit harder up front, but the DW Blasters should theoretically "catch up" and the overall damage should break even.
However, this most likely is not the case, but the classes should still be within a +/- 5% margin if Bioware is doing their jobs correctly