I tried both the 2011 iS107 and speed special W54. On the 2011 speed specials you will find enough footstrap position possibilities.
The iS107 has only 3 positions, but can be sailed wider (just move the outer screw one forward). Please do try the normal setup, with the numbers on the new straps I go up to 7. I also have 6mm boots and big feet (european size 46 surfboots), also my feet are reasonable wide, it does work fine once the footstraps are used 1-2 times (stretched/settled). It always makes me wonder how it fits on my speed special W44 tail with a foot bigger than the one foot off, but it works some way