HyperThreading or SMT as Intel now calls it, can be a mixed blessing for the Core i7. It looked to be heavily dependent on the workload, with it pulling back the Core i7 at the 4-user test scenario, though it turned out to be very useful when 8 users were chosen. In fact for SPECint_rate, having HT enabled produces higher scores than without, even with 1GB less memory. The catch of course is to have the 8 users test scenario and not 4 users. As we have mentioned in the past, the performance of HT is dependent on the application/OS picking the right core to send the workload (two different logical cores as seen by the OS may in fact belong to the same physical core). As such, for normal everyday usage, HT is really not necessary and in fact might be a hindrance as seen from our results.
Also notable from our testing is that the extra memory controller and extra 1GB memory made little extra impact in SPEC CPU2000 integer rate tests. However with the more aggressive floating-point workloads, the extra memory throughput gave rise to nearly 20% improvement in performance.
Looking at the peak scores from the speed tests, the Core i7 was barely ahead of the QX9770 for the integer segment, though the floating point test showed the strength of the new architecture. The same can be said from the rate tests as well. Overall, depending on workload types, the Core i7 can be anywhere 20% to 50% speedier than the similarly clocked QX9770 - which is quite a big leap. Even when discounting the effects of HyperThreading, the gains on the floating-point workloads can be up to 40%.