Boris,using Athlon II for future comparison isn't the best choice due to lack of L3.IMO any other 45nm core(Penryn,Deneb,Thuban,Lynnfield) with solid amount of cache will do great for future games.Bulldozer is supposed to bring another level of shared cache(L2,shared by core pairs) and with more cache and more much improved cores(8 for desktop) I bet it will do great in games.
BD scaling(the often quoted 80% figure) just means that instead of 8x perfect scaling you can look at the 4x1.8=7.2x for applications that can scale to 8 threads perfectly(like Linpack).This is around 11% penalty,in other words pretty good scaling if application is able to use the cores efficiently.