I have p3v4x with slotket.
If your oc'ing go with the pep66. If your oc'ing but on a budget and really want to save all the ram slot, go with the orb. I used the orb for over a year with no problems running a cel 600@900. Picked up a pep66 and now i can get to boot @990 and crash in windows, but running stable @945. I would recommend either.
The orb doesnt cover any slots. I actually tested the pep66 and used slot 1, but i have like 3mm between the hs and memoery chip.
Hope this helps