Presently the R2 emitter is the king of the throws.
I don't much about modifying.
Maybe you have to research the modding forum:
http://www.candlepowerforums.com/vb/forumdisplay.php?92-CPF-Custom-Flashlight-Builders-and-Modders .
Furthermore, the RRT-0 R2 already has 240 lumens.
The R5 255 lumens.
The S2 260 lumens.
Only a small rise in overall output, for very possibly a bigger fall in throw.
If you buy an R2 and wish to mod it to R5, be careful, coz the bigger emitter may not fit into the smaller orifice?
You may have to mod the reflector with a larger hole?
Or you may have to purchase the R5 reflector?
Furthermore, the R5 circuit may be different?
However, the R2 should give you the best throw of the three.
A future XM-L T6 emitter will be even more efficient and brighter, but because the emitter is larger yet using the same size reflector, the throw will be diminished.
I once compared my S2 to my friend's Maglite with conventional krypton incandescent bulb running on 4 size D batteries.
My hot spot is huge! Absolutely huge. 10 times bigger. Yet into the distant trees, the S2 beam dramatically widens and floods out.
His Maglite incandescent krypton bulb hot spot is a tiny yellow thing! Almost useless!
Yet up into the distant trees, the huge wide relector controls the sideways spill in such a way, that you see a nice tight little yellow hot spot.
Throw depends more on reflector size, especially on the ratio between the reflector size and the emitter size.
In an ideal world, we would all have a pocket rocket..