a lot of that will depend on how lucky you are, how much voltage you are willing to use, how cool you can keep them, and how good your motherboard is.
Like all overclocking, more volts = more Hz = more heat, and sometimes you get a good set, sometimes a bad one.
Not sure how these sticks in particular OC, but with starting timings of 5-5-5-15, they are unlikely to hit very high frequencies, as the timings are already very slack.
If you want an alternative, look at the 2x512MB Balistix PC2-5300, only £10 more, and their larger brothers overclock like a beast, and normaly the smaller the sticks the easier they overclock (certanly seemed the case for DDR1). Or for that matter, get the Cas4 Geil 2x512MB set, which is a mere £4 more.
