Shot a 2003 Impulse got a BKO. BKO is the way to go.
I can get 15 rps from stock, the BKO's solenoid is only 2 way so you'll be hitting its max rate of fire at about 17. Its prolly worth getting a few upgrades for your BKO:
SP mod - mechanical anti-chop
Volumiser - Mitey Max or Vapor
Vapor valve
The volumiser and valve will double gas efficiency. The SP will stop you from chopping when you out shoot your egg
Stock regs on the BKO are ok but not great. If you want to make it super smooth get a MacDev Gladiator (will need to replace the ASA bock with the 'standardised' Zentiram block) and a Palmer micro-rock. You'll be shooting +/- 2 fps.
The only problems I've had with it are the regs are very sensitive to dirt. Basically they need cleaning after a day of use.
I'll be at the walk-on in Maidenhead this weekend. If your arround give us a shot and you can do a coupel of games with the BKO....