With my old P4 (single core) HT restricted my AI to 64/2
with the ocasional xrun, HT off would allow solid 16/2 performance. My
new i5 does not have HT, so I am not able to compare.

+1 for testing + measuring.


Anyway. In most cases the CPU is not the limiting factor. In the vast
majority of cases some power-saving (bus-freq, southbridge, SMI) or
weird graphics-cards, wifi, etc and/or their drivers are orders of
magnitude more limiting.

2c,
robin