I think the Cosworth studs are fine for 99% of applications.

I know a couple of cars running them that are circa 800 bhp although they are on 2.35L (stroked EJ22T).

I went for 14mm studs because I simply had the opportunity to do so. You'll have no issue running Cosworth or ARP 625s 11m studs and Cosworth gaskets.

__________________
605whp
Quarter Mile in 10.9 seconds @ 135mph /217kph
0-100 kph 3.2 seconds