First I would start with tREF...the 166 1.95 in A64 Tweaker actually correspsonds with 2 different settings 2336 and 4708...I am on 2336.
Max Async and Read Preamble also play a part...although 9 and 7 didn't let me get even 1 MHz higher...it crashed at about 24 min through
Part of it could be CPU....this Claw clocks ram like mad.
Play with your Drive and DATA Drive...I bounced all over..your's might need more or less...remember even #'s are nomal, odd #'s are weak at varying levels. TCCD/TCC5 likes weak..but some have good luck with normal strengths.
It also depends on the Sticks....if you bought yours back when we didn't have 5 speed bins....your a lot more likely to clock high. But even now..I just got these 2 weeks ago (paid for them myself, for those that would say I got "cherry" sticks) and as you can see they do very nicely.