That is exactly what I am doing. I have xfired 4870s right now. From the looks of the benchies...the 4870x2 is pretty comparable to one 5870.
For one I will wait for DX11 to come about but most importantly, I am waiting for NV to answer back so that they can start their price wars.
Yep, I'm hanging in there with my old technology. There isn't much out there that I can't completely max out at 19x12 (except for Crysis, which can chug a little)
I'm still running XP, so DX11 means nothing to me until I invest in Windows 7.
I'm wondering how crossfired 4890s or crossfired 4870X2s will fare compared to the 5870.
As the drivers mature I'm hearing good things about 4870X2 crossfire. If the prices drop radically, and I find any new games are limited by my GPUs I might try a pair of these at some point before moving to the 5xxx series.