The older LOW wing Vipers were garbage in my opinion. The new one is completely different, and quite a bit better. If you have no intention on racing, I would personally go with a Sport Jett. You can throttle it, and you will have a useable engine if you get tired of blasting holes through the sky.

Q40's are great, and I love flying them. They will go 180 MPH + with a Q40 engine, they fly very nice, but are a bit trickier to land. YOu can see the Pole Cat at www.bigbruceracing.com it is one of the fastest available right now, but with the midwing, can be a little tricky to fit everything inside. My avatar is a Vendetta Q40 from Lyle Larson, his website is :

http://www.angelfire.com/ok2/racewithme/lylepage.html

He also sells a nice Dago Red and Proud Bird also.

Personally, I wouldn't recommend a Q40 until you were extremely comfortable with a quickie with a high performance engine.