Ok, checked my notes. The UranusFire C818 was fully modded with a UCL/p, XP-L2 V6 3B (from KD), and did:
11.8 A, 2060-1880 lumens, 116 kcd
After modding it with a 3V XHP50.2, same mods (lens, driver, wires, MCPCB, etc.):
19.0 A, 4200-3700 lumens, 110 kcd
So, 61% boost in amps, 97% boost in lumens, 5.2% drop in candela. But this is a top bin XP-L2 vs a 3V XHP50.2,
Since the C818 is a thrower, but smaller size, I think it will apply pretty well to the FT03. So there will be a loss of throw from a SST-40.
I checked the 2 reviews of the SST-40 done here on BLF by djozz and koef3 and both found the bond wires burned up at 9.5A and 9.4A, so I guess it's important to keep the amps below that level. Adding bypasses and using fully charged top cells could be an issue?