Nah you will see a bit of a performance drop from 2 5770s in x16/x4 CF. You could though save up the money now and run just a single 6870 or something and then save the extra on the motherboard. Though then you might want to CF the 6870 in the future so it doesn't really help
Just get your current config, since your only getting 5770 CF the Phenom will be fine and won't limit them.
So in conclusion, I think the best idea is to get the X6 with your current motherboard.