Since that is the "A" version of the KHX PC3200, it is using winbond ch-5 chips. You should consider searching this and other forums for info on the ch-5 chip, to get a feel for how far they will go with increased voltage (in vmodded boards, for example).
Also go to the CPU database to get an idea of just how high your cpu might go, based on the reported results from the same stepping as yours. Calculate your required fsb, in order to hit these speeds and that will give you an idea of what you've got to get out of your ram and your cpu in oder to meet this goal, and whether it is realistic.
From the database, there are 3.2s running at over 4.0, but most are under that. You have to reach a fsb of 250 in order to hit 4.0GHz. Your search of ch-5 will give you a clue as to whether it will hit that with increased voltage or not.
You might also consider this as a good time to upgrade to a gig of some of the new Samsung based chips which will run a fast timings at DDR400, and up in excess of 250 at more relaxed timings. You could end up not even needing the booster. Either way, it should be fun. Good luck.
CPU Database:
http://www.cpudatabase.com/CPUdb/
Samsung chips - ram review:
http://www.anandtech.com/memory/showdoc.aspx?i=2145