On my macbook pro 2010 2.4 i5 Snow Leopard on 640gb 7200rpm drive, Mavericks on 1tb 5400rpm drive (cloned and upgraded) in cdrom slot. I can boot between them. Geekbench 4500+- Snow Leopard 4850+- Mavericks.
I see an improvement with Mavs on my 2012 rMBP (2.3 gHz, 16GB RAM) as well. Using 64-bit Geekbench 2: On Mountain Lion: 11873 On Mavericks: 12334 I like it!