I'm not going to state anything that hasn't already been stated, just going to back-up everything the guys mentioned.
Zero balance is the way to go if you want to pay the extra dough. 28oz imbalance is the next best setup... just be sure to specify what imbalance you're going to use when you order a flywheel and balancer, as the best way to balance a rotating assembly is with these components bolted up to the crank.
I also made the mistake of not doing any research on this topic, and went with a 50oz. imbalance on the last combo I ran, and, because of current financial situation, I will be doing the same with the R-block combo in the works. I will be reusing my flywheel and damper, so I don't have much of a choice.
I will say that, even though I split my block, the rod and main bearings still looked good enough to reuse. I was spinning my combo to 7000rpms on a gear change and crossing the 1320' at 7200rpms spraying 200hp worth of nitrous. I didn't encounter any serious issues (other than pushing the limits of the stock block) with a 50oz imbalance, but could've picked up a few HP going with a 28oz. setup.
The combo I'm planning for after next year will be a serious setup... with a zero balance rotating assembly.
I will be in search of an 8 sec. timeslip at that point
Depending on how serious your getting with the new combo, you may just want to go with the 28oz. setup... ultimately it's up to you, of course.
-Ryan