You can also get Red cranks if you're not totally stuck on Force... The Red-owning crowd seems much more likely to upgrade every time some tiny improvement comes down the road. I even have a spare Red crank in 175 with the fancy new chainrings just sitting in my shed! Unfortunately for you, it's 24mm for a standard english threaded BB.

Is it safe to assume your son also lives on LI? I'd stick with standard if that's the case.