I have both of those, personally, I'd go for the XP-G as it produces pretty much the same amount of light and is a less floody beam. I will stick both on the lightbox tonight and get some numbers for you. If the weather permits and get the work done for tomorrow I'll try for beamshots too.
http://www.dealextreme.com/details.dx/sku.21037 DX MC-E dropin Lightbox 1240 lux on high 510 lux on low. My conversion to lumens isn’t all that accurate but that equates to roughly 275 lumens on high and 115 on low.
http://www.dealextreme.com/details.dx/sku.32953 XP-G R5 dropin Lightbox 1310 high 610 medium 240 low. Lumens roughly 290/135/55. Same body, same cell and the MC-E tests were done first.
Throw results
MC-E 4050
XP-G R5 10770
In general the multi-die (Cree MC-E, SSC P7, Luminus SST-360) are not as good at throw as the single die emitters simply because the smaller the source of light, the better the throw - or, more accurately, the smaller the reflector you need to make it throw. Since you were talking about improving throw, I presume this is what you are after so I'd see no point in your getting the more expensive MC-E dropin, it produces less overall light, throws less well and costs twice as much. This MC-E light throws very well (when the switch is persuaded to work). http://www.dealextreme.com/details.dx/sku.19466 Note how much larger and deeper the reflector is. Actually, the cheaper Q5 version probably throws better. http://www.dealextreme.com/details.dx/sku.18765 Which is what I ordered but DX sent me the MC-E version instead.
If you want serious long range throw, a P60 is probably the wrong place to start - the reflector can never be wide or deep enough for the purpose. However, if you want a P60 that throws well the R5 is probably pretty much as good as the R2 ones that are known for their throw.
Probably not worth getting the smooth reflector as it almost certainly won't be suited to the XP-G LEDs, in fact it may be designed round Luxeon/SSC emitters so there is no guarantee that it'll improve matters. If you do try this, I'd be interested to see the results.
Fouled up here- it was a different XP-G R5 dropin in this one and it was 4.2V only - it is the 5 mode dropin that came with this one. http://www.dealextreme.com/details.dx/sku.33549 It did not cope at all well with 16.8V and is now dead...
What I thought I was using was the 5 mode version of the one you linked to http://www.dealextreme.com/details.dx/sku.32954 which is the one I have. The single mode one has fewer things to go wrong so is a better choice unless you want the modes.