I do not know if you would gain enough to make it worth your while.... A R2 might make it 5-10% brighter....but then again, it might not. Not all the DBS R2's were brighter than the Q versions.
If you want more output I recommend putting a more powerful driver in it since the Spear has really good heatsinking, overdriving the CREE Q5 to 1.5A or over should give a big boost to it (that will decrease the emitters life some). Changing the led will only give you a marginal improvement.