If you want the boost to be there when you want it, don't go 20g
Longer spool times. Not that great for city driving.
In relation to your question on block wear, there is no right or wrong answer. Seems like a general statement would be 350whp on stock internals seems to be the cusp of safety. Even then, expect faster wear and tear on all internals. There is no magic number really. Then again, a poorly tuned stage 2 could also be detrimental at 100hp Lower.