In a lot of situations, probably not. The E8200 has a newer architecture (Wolfdale), which is the next refinement of the old Conroe generation, which included all early E6xxx and Q6xxx series of processors. It is faster per clock, and for any workload spreading to only 2 CPUs, you won't notice any improvement with the Q6xxx series, and maybe a decrease in performance in many applications and games. In sheer CPU-cores limited scenarios like video encoding, you should notice an increase in performance. It MAYBE a parallel-step instead of an upgrade.
The E8xxx series also feature a lot lower power consumption compared to the Q6xxx series processors
Your most desirable upgrades are to the same architecture Core 2 Duos, but quad core, like the Q9xxx series (pick something fast with a fat L2 cache).