I never heard that about weight limit for sf props but it makes a lot of sense - you don't want to power an sf prop so much that a blade comes off!

I have a profile Katana with 36" w/s, weighing in at 27 ounces with 2x1000mah or 2x1300mah 3S packs. I used to use sf props for the same reason as you, but now I have started using GWS HD or DD props - in fact right now a 10x6DD, with good results. The motor is a Chinese outrunner - RC1050 running at 1050kv and about 275 watts maximum. I get about 12 minutes of thrashing around. I used to use less energy (mah/minute) using a 10x4.7 or the 3.8 pitch GWS props, but I took some flak from club members who didn't want their eyes impaled by rogue sf prop blades coming off. I told them to get a sense of humour and wear protective eyeglasses, but they just didn't get it!