Yeah the memory compatibility on this board can be fussy (as with all ASUS 775 x38/48 boards).
I must admit I am also relishing to see what zsamz results are!
4GB modules would rock the socks off as having all 4 DIMM's populated does seem to significantly limit OC'ing (as I have found out by using all 4-DIMMS) and brings unforeseen results.
John