My experience has been that EXE Optimiser and MCP work fine together. But I need to use MCP first otherwise the MCP patch will fail.
This is my experience also. MCP first, then exe opt.
I can't give a real answer on stability as I started using it a looong time ago so I can't remember, I too have been curious as to whether it's still necessary. Suffice to say I currently use MCP and the exe opt (along with MWE, MGE, FPS Opt) and my game is the most stable it's ever been and that's with ~250 mods installed.
-kwm