the moment you get on a 400-series hwy
I consciencely avoid the 400 series highways unless I need to get somewhere. Part of motorcycling is looking for roads less travelled. If regular use of the 400 series highways are a reality, I say stick with a cage.
I don't even like my 1200 sportster on the 400 series.
A 250 is great to learn on and will provide plenty of pep for anyone. I think about those folks that look to upgrade to something bigger so they can keep up. The fact is, you know you've got enough seat time to upgrade to something bigger when you are keeping up or exceeding the pace of others on larger machines.