Hi Wayne:
The latest 993 TT dilavars have been very good and I use them in everything. Steel studs are OK too for early (non-mag) engines that do not get hot,.....
They are quite strong and reliable of course, but they cannot accomodate the engine's expansion very well and in the big-bore motors, I see some leakage from the head-to-cylinder surfaces due to bending when hot.
I don't use Raceware or ARP studs any longer due to head loosening issues.
Nathan:
You can turn the engine up to 7100 if you have the ARP bolts but unless you make some cam changes, its rather pointless.