FWIW, I had a burton custom back in 2003 when I weighed about 190-195 and I'm also 5'8. It was a great all mountain board. The only time it gave me a hard time was when I caught a storm in Utah with 8-12 inches of powder each day I was there. Manageable with a fresh wax though. I'd only go bigger if you were getting a powder board. I had a ride timeless that was a lot stiffer that was size 155. If it's a stiffer board you can go 155 and softer go 158.
I've never seen anyone use a foot size to choose how to get a board. I think weight and muscle density is more improtant IMO. I bet we can use the same size board I use and I weigh 225-235 and I have a size 10.