1) Probably yes. No longer having to use the FSB/QPI to send messages between two pairs of cores should make an appreciable difference.
2) Almost certainly yes. RAM is accessed a lot for the SMP client so speedups here should be noticable in folding performance.
3) Yes, same reason as 2)
4) No. The Folding@home client will load all four physical cores on each processor, thereby stopping any being powered down to allow others to be boosted.
5) Maybe, as the current client uses the localhost which invokes the networking hardware.
6) No difference to SMP, obviously. I don't know anything about the GT120 but the HD4870 will add a not-insignificant amount of points to production if it can run.
There are only 8 eight real cores, so for the purpose of Folding@home SMP it is an 8-core machine. The a2 core supports scalable threads so can work with the -smp 8 flag to utilise all the CPU power with one client. However the a1 core which is still in use is locked to four threads so to ensure 100% usage at all times it might be necessary to run two clients with -smp 4.
Nice to see another member from around my neck of the woods