My first choice would not be Kohler, but that's another story. Look at the detailed spec sheets - you may have to call Kohler. They will list gpm at a certain pressure for each valve. Figure out how big of a tub you want to fill, then decide if the minutes saved is worth the extra money the larger valve costs. Only you can decide on the cost/benefit breakpoint. It somewhat depends on how big the tub is. What's your tolerance for the time it takes to fill it up?
Kohler makes some nice stuff (and some I think is lousy!), but because they do not have a standardized set of 'guts' they build off of, replacement parts tend to be hard to get and expensive. This is opposed to someone like Delta that has relatively few 'guts' and then just changes the trim...when it comes time to repair it (and all eventually need something replaced), it's cheap and readily available for the most part. Kohler is infected with NIH syndrome...plus, they always seem to think they can make it better (which in itself, isn't bad, when done sensibly), so their designs often end up weird, and when they don't actually work out well, changed often. Ask a supplier to look at their parts catalog...it looks more like a big city phone book - the main reason nobody stocks many Kohler repair parts.