I tried it on a Mid 2007 MacBook Pro with only 4 GB of RAM yesterday and it ran very fast, but it has an SSD in it. Seemed to run even faster than 10.6.8.
I have it also on a white MacBook 2010 with HDD and 4 GB RAM. It's not really fast, but not slower than older OS X versions.
You have 8 GB RAM, that seems to be enough to run it without an SSD. Just try it on a second partition first.