There is nothing futureproof about any socket 939 processor. They do a fine job at what they do but AMD basically signed socket 939's death warrant with yesterday's release of socket AM2. Seeing the performance of AM2, I'm glad I have my 939s though that performance is going to change rapidly. Once AMD gets everything over to 65nm, clock speeds will ramp up quickly and the K8 architecture scales marvelously. Combine these higher clocks with the additional bandwidth of DDR2 and AM2 will be a real winner. Conroe may get and keep the crown for a while (and again, maybe not but until it ships, it doesn't exist.) but AM2 will be in the running to say the least!
But, now is not the time to think "futureproof". Either buy obsolesence now or wait. This isn't to say that you can't get some extremely powerful stuff right now, but you will be limiting your upgrade paths.
Almost forgot, there is some interesting information here
that may help you answer your own questions.