Help with compatibility

I have a ASRock 939Dual-SATA2, with a HIS 4650 AGP.

i am about to upgrade my other computer from a PCIe ATI 4830 to a PCIe AMD 7750 or AMD 7850.

I would like to take the 4830 PCIe and add it to my system with the 4650 AGP.

Can i do it?

would having both improve performance?

Would having both be able to crossfire (over the bus, seeing that the agp model doesn't have the CF bar.)?


ps. the mobo supports a feature where it can have an agp and PCIe card and each have 2 monitors. in the CD manual given uses mixed matched cards and allows them to display one desktop.

1. Gigabyte R9200 + Gigabyte-R-X600Pro
2. Winfast A340TDH + ASUA-EN5750

pss:
Links to Mobo and My GPU
Mobo: http://www.asrock.com/MB/overview.asp?Model=939Dual-SAT...
4650: http://www.hisdigital.com/un/product2-480.shtml
4830: http://www.hisdigital.com/un/product2-386.shtml


Any Help would be appreciated