SpringHeeledJack,
The honest answer is its hard to say.
From a technical point of view, since OS X is a BSD based platform, its quite efficient anyway. In terms of the OS X improvements 10.8, I think it was one of the best OS's yet in terms of optimisation and stability.
Perhaps the other important element to consider is software and security updates. 10.6 has almost certainly lapsed and OS X 10.7 probably heading that way although one or two updates were released for it in 2013.
I would probably go for it as I'm fairly confident there shouldn't be any performance issues. However I would say make sure you have good backups, and make sure you check with your third party software suppliers that their stuff is compatible with whatever you decide to (most stuff is and stuff that is not can generally be updated).