Getting second 4870 or wait?

hey guys I sold my old case and processor on ebay and I thought I could get another 4870 to my system....do you think its worth it or wait for 5xxx / 3xx gtx cards to come out and get one single powerful card?

my system is as follows

*G.Skill 4gb ddr2 800 @954mhz
*Vista 64bit
*Intel Core2Quad q6600 @ 3.4ghz
*Antec TwelveHundred full tower case
*Silverstone 700w modular striker series
*ZEROtherm Nirvana cpu cooler
*Power Color Ati 4870 1gb ddr5 edition (800core/1090memory)
*ASUS 20X DVD±R DVD Burner
*Seagate Barracuda 500gb HD (2x)
*P45 ASUS P5Q pro
*Acer 22" (1680x1050)