i can run my corsair kit down to 54 tRFC
guess it all depends on the board and kits

i've seen a few people benchmark 7-7-7-x or 7-6-x-x- on 790i at 2GHz which is encouraging.............

i reckon it's just going to need some more bios tweakin by engineers but once CAS7 and CAS6 clocks get up to speed Superpi times will tumble even more....you would definitely beat your old score in this category with CAS7 imo