How well does Mezzmo make use of multiple cores?

I have a Xeon E5-2670 v3 box I could use for Mezzmo- this is 12 cores with two threads each, for 24 threads; the CPU runs at 2.3 GHz. It would be running Windows 7 / 64 with 16 GB of RAM. This CPU has all the latest SSE and AVX instructions: MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2, FMA3, F16C

The alternative would be to use an i7-920 running at 3.8 GHz. This has four cores with hyperthreading, so can run 8 threads. It has support for MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2 instructions sets.

If Mezzmo would make use of many threads running on multiple cores, the Xeon would be the better choice, generally speaking. If Mezzmo is just going to use a few threads, then the faster i7-920 would be the better choice.

Typically, my current Mezzmo server (Core 2 Quad 9950 2.8 GHz, 8 GB RAM) is transcoding-on-the-fly a 480i video and serving it to one device; occasionally there are two devices connected and so transcoding and serving of two 480i video will be taking place.

I know it's hard to predict performance, there are so many variables. I guess what I am asking is, what helps Mezzmo more- more threads or faster raw CPU clock speed?

Thanks