linpack is so arithmetic intensive that all HT does is cut the amount of cache in half. it's just overhead. the amount of operands accessed from main memory is usually under 1%.

http://www.anandtech.com/show/3470

on the other hand HT can increase performance by up to 70%. with the 3rd channel it's easily 2x faster than other 45nm processors.
http://blogs.sun.com/4HPCISVs/entry/..._on_nehalem_an