If UAC is on and you aren't the local (built-in) admin account, yes.
If you run a process explicitly with a high token, then it's integrity is set to HIGH, and protected mode is off.
IE x64 would be generally more protective than x86 by design, but prior to IE10 you paid a javascript performance penalty for doing so. IE10 actually runs the IE process as x64 and tabs as x86, which is done for security reasons, so you don't have to explicitly run the x64 version anymore - it'll do it for you regardless of which one you choose.
