X48 = best of the crops. Overclocks great. Choke full of the latest bells & whistles.
790i = has issues with corrupting sata raids when overclocked. If run at stock, it's fine. Only supporting ddr3.
780i = best budget SLI board. Supports ddr2. Can do 3-way SLI.
Out of the 3, hands down X48 the best chipset. It can't SLI. I think the best would be X38 with 9800GX2 which beats out anything else in SLI. X38 supports DDR2. Cheap & abundant. Good examples are GA-X38-DQ6 & Maximus Formula.
I'd avoid the 7x0i for anything but a pure gaming rig with instant SLI benefits. As akhilles said X38/X48(it's the same thing) is as good as it gets.
I'd also stick with DDR2 for now. DDR3 offers miniscule improvements for a heavy pricetag.
I've got a Rampage formula for about a week now. Greatest Mobo I ever owned. I heard a lot of people complaining about stability issues, mine just works fine.
I have a Q6600 ( until the 9450 prices will come down) , 2G of Crucial Balistix, and BFG 8800GT on it.
System booted at the first try. I just put all the parts together, reset the BIOS, started the PC and "voila".
Most interesting part: the board knows how to set the voltage for the memory. By default, the timings were 5-5-5-18 and the board gave 1.945v to the RAM. I changed them to 4-4-4-12 and the board gave 2.2V to RAM
What can I say? This board is an over-clocker dream
I am going to get the 790i board as well. But I am just trying to decide between the Asus and the eVGA. I know the Asus has a few more features than the eVGA board. On the other hand I have seen some negative stuff about Asus. Like them lying about some stuff. Plus I have been with eVGA for a while now. I would go with the x48 chipset but I want the 9800 x2's. I am getting 2 of them. I will pairing the board up with the QX9770, OCZ PC3 12800 RAM @ 4GB. Put in the Antec P190 case. If anyone has any other thoughts for a case please let me know. I also want to get the new Creative PCI-E card here: http://asia.creative.com/products/product.asp?category=... So price aside which brand would be better?