Originally Posted by
lambo_vt
If you can't brake hard enough to spectacularly wreck with a front disc, something is wrong that's not the disc size.
+10 - I ride a Surly Big Dummy cargo bike with me and my GF on board [300lbs + 40lbs of bike] I can stop easily with Avid BB7's and 160mm rotors. Surly notes that going to larger rotors is unnecessary and if you apply to much braking force can damage your frame/fork.
If that was my bike I'd sort out what was wrong with my brakes as they are rather than spending $$$/time upgrading the rotor which may well not solve your problem.