ok found info and loads of information on this subject
works on Asus A8N-E 4x slot and also 16x slot (didnt no this myself fits 4x slot)
works @ 4x on an Asus A8N-SLi Premium (look like ill get this board)
doesnt work on Asus A8N32-SLI (how strange considering its 2 x 16)
only works 1x speed on a ultra d 2x on the newer models and MegaRAID SCSI 320-2E needs 4x @ least
so seems only the Premium that will give 4x s mabyae a couple of others
its more down too bios support from manufacture but the earlier revison's of the nforce4 chipset will only work @ 1x (capacitors on chipset not correctly setup) for the sli bridge
so for the MegaRAID SCSI 320-2E to work it needs 4x slot or a motherboard that gives split 16x + 4x on the sli.
looking at most of the DFI mainboards none of them will work, not even the expert as these only give 1x or 2x @ most on the other sli.
@ tomos: the card you can get for about £400 brand new mabaye cheaper if you no people who can get this kind of stuff, also il be selling the componets to put towards the card.
and theirs a bad batch of the cards on ebay so avoid, aparently there prototype models for dell wich dont work, something to do with ITBBU cache not enabled so make sure the card comes with ITBBU cache Module because then you can flash the firmware.
hope this helps
james