With that type of performance and driving, I agree with your decision to not use long drain intervals.
I've used German Castrol 0W-30 for the last 3 years or so in my stock LS1. I've noticed better pressure and less noise than when I used Mobil 1 10W-30. I don't put a lot of miles on the car, and change it once a year (usually about 3k miles). More often if it sees the track. I wouldn't use any other type of Syntec - IMHO it's underperforming and overpriced.
You can stock up on GC right now for $28 - five quarts with a K&N oil filter, arguably the best oil and oil filter available for the LS1. I'm sure both Amsoil and Redline would be excellent oils, but at the GC price point, it would be hard to go with anything else. There must be a thousand Autozones in the LA area so it must be available. It's plentiful here in Vegas.
Where the "boutique" oils shine is in the rest of the drivetrain. I recommend filling the stock differential with AMSOIL SVG. At that horsepower, it is at its limits, if not beyond. Not sure about the tranny - if you find the best fluid for the T56, let me know as I'm about to change.