Although we can't rate Ivybridge performance until it arrives, if you're after a gaming platform you're not going to be at a significant disadvantage if you get Sandybridge now. There is zero basis for Ivybridge being useless...it's more power efficient and because of Trigate it will likely overclock more efficiently than Sandybridge.
As aicom said, RAM isn't an issue. I use 1600MHz RAM on my system, and depending upon your motherboard you can go right up to 2133MHz (IIRC). However, for gaming, the difference between 1600MHz and 1333MHz for RAM won't be discernible.
Your options are really to buy now or wait until Ivybridge comes out. I'd recommend heading to the Home Built section of the forum and filling out the form asking for build advice.
An SSD is a good move too...it makes your system a lot snappier.