Question Getting New Processor

I don't guess I can say that I am new to the overclocking game but I have been out of it for a while. The last overclock I did which is still going strong is a PIII 600 @ 800 stable for more than 3 years I guess that it works. Anyway that is my standby computer right now I am running a 2200+ on a NF7-S Rev 2.0 with decent ram and was reading here and there and everywhere thinking about getting a new processor and decided to go for a the 2600 XP-M my question to you guru overclockers is which stepping to get, I can get one of these 2 garanteed so in your alls opinion which do I get.

AXMG2600FQQ4C-IQYHA:0348TPMW
OR
AXMG2600FQQ4C-IQYHA:0348XPMW

I don't know what the difference is and want to know which one to get that may be better for oc'ing I think they will both do fine but I just want some kind of clarification.

Thanks

save some money and get a 2500 M

? 2600 cost more then the 2500