Matching CPU's MP 4,1 Yes or No?

Hi all,

So I've searched the forums here for this subject and the results I've found seem to vary somewhat.
I've got a dual cpu MP 4,1 that I want to perform the well documented upgrade on. I've also got a single x5690 cpu, can someone tell me unequivocally that I could by a second non-matched x5690 and it work? Has anyone on here done this and succeeded?

Any help much appreciated,

Thanks,

J.