The “P7” LED light should be much of a muchness between there performance in my book, so the cheapest of those two is ‘probably’ the best (though I’d wonder how well the battery is sealed on the cheaper one – but that can be sorted by DIY).
Though personnaly I’d prefer a 5 mode version, as the “low” modes on the 3 mode jobbies is useless, where-as the medium modes on 5 mode light is much more useable (for non-technical bits) and will extend the overall battery life on a ride.
BUT the other option you’ve missed out, are these:
http://www.dealextreme.com/p/t6-assault-crown-waterproof-xml-t6-3-mode-1200-lumen-white-led-bike-light-with-battery-pack-set-82508
Which are much brighter and have more throw, though some ppl don’t like the very bright spot effect & little spill.
As above both the P7 and XM-L unit are available in the UK for a little extra money – delivery tends to be quicker (DX get back logs come later in the year) & supposedly you get a better/quicket UK support