I can't locate Sugino's USA website, and a quick check of e-retailers appears to indicate the longest crank available is 175 mm. Is that correct? I'm about to order a touring cycle, after waaaay too much head scratching, and I'd like a square taper crank mated to a Phil Wood bb. I want to avoid splined, integral bbs, "octalink" and whatever other wonky "improvements" are out there in favor of time-tested simplicity.
time tested simplicity aside, all the improvements you mentioned are actual improvements. This is one of those rare situations in which the latest improvement is, by most accounts, actually the greatest. It sounds like you've already made up your mind, but if you haven't I'd suggest the shimano dura ace or deore xt cranks, both are available in sizes to 180.
But, to your original question, I've only ever seen suginos in 175. Long cranks are pretty specialized. god help you if you need longer than 180.