The Athlon XP rig is limited as far as upgrading goes. The XP is near the end of it's yield and my guess is that the next offering from AMD (hammer??) will not work in your current mobo, so you will be linited to the 2000+ or 2100+ tops. The 1.6A at 2.1 or 2.2 (almost a sure oc) will be almost equal to your 1700+, BUT you will be open to future Northwoods, most likely going into the 3's. I say go for it, but I am not an AMD expert by any means, just going by what I read.
Getting a 600mhz overclock out of a Northwood is alot of fun and very exciting. Makes you feel like you got a 33% faster chip for nothing. The XP+ doesn't oc nearly as well, if at all.
LJ