I've been hard on Royal Purple in the past, but I do think their racing oils are pretty good. It would be nice to see a bit more ZDDP in them though.
I'd especially love to see the RP41 (equivalent to a 10w40) in an LS1 engine. Although this RP21 might do well in there also since it's on the thicker end of the 30wt scale.
How much does this oil cost compared to their multigrade street oils?