I deal with these on a regular basis... mostly on SBF strokers. As the guys said above setup is EVERYTHING. The majority of them that come in running poorly have throttle plates that are out of sync.
Spend the money on a good EFI system with someone that knows how to tune it. #2 problem I see coming in the door is guys that tune them to run like crazy at WOT but can't tune them for part throttle operation or drivability. The MAP signal on these systems is narrower than on a common plenum manifold so the part throttle driving runs through the same spots as hard throttle. It takes a lot of experience to dial in the enrichment tables to get the drivability right.
Mark will tell you that ACCEL is the way to go... I have great luck with FAST XFI systems.... most importantly is that you have a competent tuner to set it up for you. I've done a couple with EZ-EFI gen1 and not had good results- my theory is that it goes back to the "bubble" running through the same spots on the fuel tables and the system tunes in glitches. I've been talking to David Page at FAST about the Gen2 EZ systems and the Sportsman systems and almost pulled the trigger on a Sportsman for a current ITB Windsor project but they won't be releasing them for another month and I can have an XFI on it by the end of the week.
Another thing I highly recommend but I know it comes down to visual personal preference is the filtration. The UP cars were built with DC&O ITB manifolds with the spun stacks... the filter media they used was horribly restrictive and breaks down over time. On a Keith Craft 427 SB stroker we gained 40rwhp simply by taking off the filters. We developed adapters to bolt on KN filters that only cost 5hp and never break down.
They are good if done right and short of dropping a couple turbos under the hood it's hard to beat the cool factor.