difference in Athlon XP 3200 Barton vs. Athlon XP 3200 TBred-B...

what i've noticed is the differnce in the cache. Barton Core is 512KB Cache, and TBred B Core is 256KB Cache. i lost an ebay bidding on Barton and now only have TB left as an option. the guy who won paid $80 which is nice but it pisses me off cuz i wanted that chip really bad and was willing to pay even $90 for it.

now another difference is that the guy says that overclocking on the Barton is 2500MHz (3600+) @ only 1.80v @ up to 52°C. and on TB is 2500MHz (3600+) @ only 1.875v @ up to 52°C.

so in the end does voltage and cache difference make that big of a difference with or without overclocking? because i have an old system from 2003 and i want the best possible chip possible. even if it has to do with some minor cache difference being twice as less

my system is:

Asus A7N8X
3 gigs of Corsair RAM, one of which is XML serious for overclocking
2100+ Athlon XP TBred CPU
2 HDs - Master is 200GB Segate (IDE) and 500GB WD (ATA) as slave
ASUS AH3650 AGP video card (just installed it yesterday)
Coolmax Model AP-550X(A/PFC) CP-500T PSU
2 LG DVDRW's (i turned one off today incase it takes too much voltage)
WinFast Dleadtek TV card
Red Thermaltake Lamp
5 Fans inside my PC
1 little fan on top of RAM
& 2 HD cooling cases that each has 2 small fans on it spinning and cooling the HD

what do you guys think? i got about 1 day to make this decision and if TB is not as good then i dont want it. i simply want to make my old pc a powertank for playing World of Warcraft cuz its the only game i play nowadays. i dont want to spend $1000 on a new pc cuz i dont need it so i want the best out of my old PC i put together myself and squeez every power out of it.

p.s. what does it mean when it says "Multiplier is UNLOCKED"