Until now I've never really had enough cores in a box to worry too much about allocating multiple vCPU's but now that I have 2x6 core 5600 CPU's in my new vSphere hosts it's something I can consider.

We've had high core counts, decent single-core performance, and thermally efficient CPUs for years now. Comparing an 8-year-old CPU to a modern chip will show you a huge performance gap, but ...