Two RCR123A cell will be drive the EO-9 at its brightest, whitest and most efficient (outside of a host supporting 2x17670, or 2x18650 cells). In terms of sheer output, the EO-9 will absolutely eat up the M60 indoors and obliterate it outdoors at any distance. The SR-9, or HO-9 would be better candidates for an equivalent comparison.
I'm using 2 RCR-123A so they're only 7.4v, just wonder how it can get the best of 9v bulb? Do you have a link for SR-9? Where to get the lowest price?