Dart blocks come in two bores, 4.000 and 4.125, and I have heard they can be bored out as much as 4.2" but like a 302W, you can bore it out to .060 and even larger but it's recomended to stay under that. I am sure that those guys with the big fast turbo systems probally are running something else besides 302W blocks.
Turbo is the way to go, no doubt. It is also very pricy, but then again you get what you pay for. I am at a crossroads, building a Dart 9.5" deck motor, most likley a 427cid nitrous motor, but then again, all those bottles is going to add up, and it won't be there except when the bottle is open and loaded. I am thinking turbo, but the cost chokes me. Turbo, intercooler, BOV.... it adds up fast. A basic junkyard setup is cheaper, but then again, a well setup turbosystem is much better.