If you're still using a spinning hard drive, it'll probably seem slower. If you have an SSD installed, it should be just as quick if not quicker. The HDD is the real bottleneck in these older Macs. Plus the drives themselves are getting old.
For what it's worth it runs perfectly fine on my 2007 iMac, which is a base model from 8 years ago but with an SSD installed and 4GB of RAM.
You can stay on ML for longer if you want but El Capitan has a lot of security fixes that aren't in 10.8. And it'll be getting more updates. If you plan on keeping this MacBook I would highly suggest an SSD. If you don't have a lot of data it's really attractive with 120GB ones going as low as $45 on Amazon and 256GB ones aren't that much more. They help an awful lot with booting up and loading apps. Plus if your HDD is 5 years old it would be a good preventative measure. Always have backups though!
From my experience with my iMac (128MB 2400XT) and 2008 MacBook (9400m) Yosemite was a bit slower than Mavericks/ML graphically (dropped frames with some apps due to the translucency), but not much different performance wise when using applications.
I'd say give it a shot with either the GM or the final when it comes out soon.