[MiNT]

Glad I could help =] Try merging everything over into a new file and saving as a new file, that may clear things up.

As for your model, I notice the mesh density is pretty high (duh...you say) - are you using meshsmooth on it?

If you're not, a quick fix would be to use an 'optimize modifier'. Turn the renderer setting to 'L2', and leave viewport on 'L1'. Then just fiddle with the threshold until things work a bit faster. Oh and you may not want to be working on the mesh while the optimize is active. To turn off the material in the viewport, you can do it in the material editor by material (fourth button from the left, checkered box button) by clicking the show in viewport button. Finally if you're really not using some of the objects in your scene, select them, right click in viewport and go to properties. In the first menu somewhere is a checkbox for 'display as box'. This makes it annoyingly hard to select though.