Christian, the fact that you can not see tha graphics should not bother you. They work in some comps, in quite a few they don't. In my herd the graphics work on all Intel machines, but only on one AMD. I do not know if that is typical.
About speed: that sounds right. On my A64 3200+ a WU takes about 65 - 70 minutes, so yours should be around 55 minutes - which it is. Please see the very first post for speed info.
If you want, look at your results in seti - if you have some from the time before you switched. that should give you some perspective. The maximum speed I have seen posted is 45 - 48 minutes for a WU - on a A64 4400+ with a optimized application - so you are not far off at all.
With a standard application it would probably take almost twice the time (I guess...)