You may be attached somewhat to unity but I'm with moparman. Unity is plain slow. Sorry, but it's true. There have been complaints about unity and compiz performance since they came out.
My i3 laptop could play 1080p video just fine under windows 7 but not under unity. Gnome classic is faster but it's not very configurable.
I tried ccsm settings but I just don't like having to **** around with settings that can make the system unstable. It kind of worked but the system felt glitchy afterwards.
I haven't tried lxde but I recently installed xfce over ubuntu 12.04. It's fast. I mean snappy. it's not quite as plug and play but it's also highly configurable. You have drop down application menus and can also set up custom launchers, which I far prefer to having everything on a huge list.
Also, it works better. The dual monitor support actually works properly. In ubuntu and gnome only extended desktop is supported. If you have an external monitor plugged into the laptop and you close the lid to suspend you lose cursor control and have to do a hard shutdown. If there's an answer for that I can't find it. Xfce does not act like this.
I just don't think unity is suitable for old computers, any more than windows vista is.