OK, I've finally gotten around to beefing up my stock Early 2011 17" MBP. Upgraded the RAM to 16GB and I've got a SSD to replace the spinny 750GB model that came with it. The machine came w/ 10.7, and ...
If you won't have any space issues on your 500GB drive (and it doesn't sound like you will since you're only using half of it right now), then it makes more sense to leave that OS X installation on ...