440bx?? Dude, the skys the limit.
If you wanna really have some fun, check these out
slot one to socket 370 tualatin adapter and here is the compatability
list clearly showing your board works with this thing
You could get the adapter, then a used celly tualitan..like around a 1.2 gig..I got a nice used one off of anadtech forum.
Thing would scream.
I just bought 2 of these "slot t" adapters...one like the linked one and one made especially for dell gx1's...at first I was miffed...it wasnt working...then I DOWNGRADED the dell bios from a10 back to A07..and it works! lol.
Or if you have a regular slocket you can get things like
this which would allow you to use regular ppga cellys.
Either way, bx boards have lots of upgradeability. Just remember when you are overclocking the fsb you are also overclocking the vid card and pci cards etc...so sometimes they hold you back and not the cpu itself.
JP