This may sound a bit overboard, but I've got a P5 that I use for loose tracks and club races, a Hott Mods 528 for big races, and a second stock 528 for, well, just to have around

IMHO, if you're going to have just one engine, you should take a good look at what other local racers are running and make your decision based on that. Not everyone needs a .28 to win - look at Jammin team driver Chad Bradley. He ran an OS V-Spec (.21) to win the RC Pro finals at Sun Valley which had a tight infield and a 220' straightaway.