Although I'm sure CoFH Tweaks had a disclaimer about being incompatible with both Fastcraft and Optifine.
I just rechecked that and could not find anything of the kind anywhere. In fact the only documentation I can find is a feature list. Gonna suggest the same thing to them when I get around to that.
For now i just booted CoFHTweaks and went with FC + Optifine.
thx m8s