The X-LM is rated for 3A, it is a 10W LED. (The XP-G is 3W though, if I remeber right.)
Overdriving XM-Ls up to 4.5A has apparently been tried, but proved pointless. Although it didn't destroy the unit, which gives a good indication as to the build quality and potential longevity.
Personally I underdrive mine at 2.1A on a passive (at the moment, I'll get around to sealing the water leaks one day, I promise!) heatsink.
I would be surprised if the chinese 10W LED's put out anywhere near the same PAR, the efficiency of those larger die units is not as good as the top of the line CREEs, and more surprised if the CRI (colour rendition index) was even in the same league.
I'm happy to read evidence to the contrary as it will make the rest of the conversion of my tank that much cheaper.
create random acts of beauty...