My only concern about keeping your IP35 is the lack of anything from Abit since they're out of business now, so no support, no RMA, no updates for BIOS, etc.
As for the speed, it may, and that's a big MAY, make a difference.
As for the board, the Rampage is a great board, despite a few peeps hating on Asus, myself included. But my despise of Asus is centered on their video cards, after having the last two Asus video cards die in less than 6 months use without any overclock or overvolt to them (3870 TOP and 4850.) RMA for both was horrible taking over two months each time and had to repeatedly returning the card I received from RMA.....and those were the same broken cards I sent in without any fix at all.
But for Asus motherboards, I prefer them over all and still buy and use them.
On the other hand, I've heard good feedback about the Foxconn Black OPS X48 board which is quite inexpensive (relatively speaking at least) at $89.99 AR from Newegg ($119.99 before rebate.)
http://www.newegg.com/Product/...x?Item=N82E16813186144