Everyone I know has been 110% satisfied with the Whipple system. Most of the high performance engine builders out this way seem to agree that the Whipple system is the one to beat right now. They've got the ECU dialed in and it is ultra smooth. I went out in my friends 27 Lavey cat with a Whippled HP500EFI two weeks ago. HOLY SMOKES BATMAN!!! It flew! It also idled for as long as you wanted with absolutely no sign of there being a supercharger under the hatch. In fact, the boost guage didn't even show us running in boost until about 3800-400 RPM. And then look out!!!
If you want an honest opinion from a very well respected mechanic, call Jim Wilkes at Wilkes Marine in Santa Ana, CA. Jim will talk flat out and honest with you about all of the different blowers on the market. After all is said and done, he recommends the Whipple, even though he is best friends with the owner of Vortech Marine. I don't have Jim's number handy, but if you have a copy of Hot Boat magazine handy, look under the V-drive tech section. Jim is the guy who answers all of these questions. His number is there.