There are no pissing matches, just different experiences and all are valid. And true, the OP needs a plan or to set goals. Otherwise it'll be an endless experiment trying to get the car where you want it.
As for my $.02, if you want to chase ultimate HP, whipple or tvs it at a great expense. But that's just me, I love the SC over a Turbo. But Turboing the engine is a better bang for the $$$. The M90 is terribly inefficient, but we all trade efficiency by dropping pulleys for more boost. There is a crossover. Is why intercooling or high octane race gas (through whatever means) is utilized to offset some of those inefficiencies.
On an L67 it is better prepared for the higher boost as mentioned, piston ring set up being one thing not mentioned. And yeah, the lower compression will create less HP, all being equal otherwise, but also better suited to handle the higher boost of the Turbo. It's a game of Russian Roulette because if you go the route of chasing HP, you'll go until you blow! Lolz...
Then of course there's always the glass tranny to keep in mind!
: )
Good Luck!
