I'm pretty confident that the difference in games from a 3.8GHz (awesome clock btw) quad to a (let's suppose you get a good one) 4.6GHz dualie wouldn't be much. I've just upgraded from a 3.2GHz E2180 to a 4.2GHz E8500 - that's a noticeable upgrade in games and at the desktop. 
I'd be very happy with your processor at the moment, the only reason I didn't go to a quad is heat as I've got a small form factor gaming rig and I couldn't afford a 45nm quad. (I think I'd be happy with a Q6600 at 3.4GHz over my dual core if the quad only kicked out ~80W under full load)
Just my opinion, obviously no one can tell what will perform well in generations of games that aren't being developed yet, but I'll take a leap and say that I think having 2 more CPU cores will be more useful that a few extra MHz in games and apps to come.
I doubt your quad's clock is bottlenecking your GPU in games too, to see a performance boost in games you'd be better off upgrading your GPU.
Again, just my opinion
Hope this help,
Banjo

I'd be very happy with your processor at the moment, the only reason I didn't go to a quad is heat as I've got a small form factor gaming rig and I couldn't afford a 45nm quad. (I think I'd be happy with a Q6600 at 3.4GHz over my dual core if the quad only kicked out ~80W under full load)
Just my opinion, obviously no one can tell what will perform well in generations of games that aren't being developed yet, but I'll take a leap and say that I think having 2 more CPU cores will be more useful that a few extra MHz in games and apps to come.
I doubt your quad's clock is bottlenecking your GPU in games too, to see a performance boost in games you'd be better off upgrading your GPU.
Again, just my opinion

Hope this help,
Banjo