That's what I've been using, their motorcycle specific one I get from an independent Harley repair shop. My analysis from Blackstone Labs has been very good so far and it hasn't pulled "A Robert" yet. Hopefully it won't either. No squealing clutch or shudder either.
There are some photos of the inside clutch area when i did the chain jump guard on this site. It was very clean and I didn't see any yellow varnish anyplace. I looked t the clutch pack for any indication of the plates cutting into the basket and didn't see anything there either. Cam chain tension was tight on both sides too so the tensioner must be holding pressure so that was good I guess.
I'm using their gear oil stuff in the final too. Hasn't chunked-out or leaked yet either..knock on wood. Blackstone is clean on the report their too for any sundry metals contaminating the oil (like chrome off some ball bearing).
I used the Amsoil for a while on my 08GT, it's good stuff, but I was still getting clutch squeal. On my last oil change I switched to Castrol and I'm getting almost no clutch squeal, I don't think it's because Castrol's a better oil than Amsoil but that the 5-40 is better weight for the GT's clutch, YMMV