I notice that you're linking to Anitec, which I'm assuming you're living in Vancouver.
In that case, if you want simple guaranteed O/C, Netlink (NCIX) sells O/C kits. They don't include the faster sticks of RAM though, but it is good enough (in the case of the P4, using a divider).
NCIX Overclocking Kits
I'm not 100% sure they guarantee the O/C, but I'm pretty sure they do.
I should have taken a look at it, I got my XP2500+ (from Anitec actually) and it won't do more than 2.1GHz (XP3000+)