The performance is so similar that I wouldn't spend extra $20.
Tests were done with both in the AMD section that prove this.
Don't forget:
Thermaltake bad
Thermalright good.
As for the Vantec, Thermalright is better, but I would leave things as they are at 2250 on your system if I were you.
2500+ mobile would give you 2.5 GHz and that would be a real improvement, not your current CPU + any heatsink. Is it worth wasting time to sell the old CPU and buy the new, it's up to you.
Athlon 64s are about 25% faster than Athlon XPs at same GHz on average.
Save up for an affordable Athlon 64 mobo-CPU combo, if you want a REAL jump in performance.
I have a mobile running at 2.4 GHz that I upgraded from 2100+ B. I had to do it because I needed an extra CPU but it wouldn't have been worth it otherwise.
I'll stay with my system this year, maybe even next (unless DVD burning pushes me to get a 64.)