I think it boils down to what Autocad program you use, and is it multi threaded so it can use all 4 cores of the Phenom 9750. If not, then I would go for the 7750BE and Asus M3A78-T, since it has SB750.
If you can use all 4 cores, then I would add a few more euros and get the 9850BE. In the US, there is only a $5 difference between the 9750 and 9850BE.
I use autocad 2008. I don't realy know how efficiently multi-threaded the program is. In fact I don't know if it is at all. 9850BE is almost 20E higher in price here in Greece. Not much but it gets me out of budget. About the mobo should I consider choosing one with AMD chipset or stay with the nVidia one, since I am buying a 4850 GPU as well? I cannot pick both M3A78-T and the Phenom unfortunately, so are there any alternatives?