My wr250r tops out at 139km/h on gps with stock gearing, with me leaning over the handlebars (im 2 meters tall) When given +2 teeth on the rear sprocket, I can clutch up wheelies in 3rd gear, and still cruise effortlessly on anything but the interstate.

Not my definition of underpowered.

The air intake is opened up, and theres a different exhaustsystem on it, thats it for power mods. The stock exhaust can be modded for juuuust about the same gains)

You will, however, notice the lack of torque, compared to a bigger bike, but that goes almost without saying. I have both my Xt600, and a wr250r, have many times considered to throw a better seat and larger fueltank on the wr, and use it for multiday/week-long trips. The bike is plenty capable.

I use mine mostly for daytrips and regular enduro, helping as a trackmarshal in our nation championship, but also a few weekendtrips.

A 450f would also be a great choice, if you can live with the few downsides. Luggage can be sorted out, gearing can be chanced, but youre still looking at a bike which needs oilchanges meassured in hours, not thousands of kilometers. I've only tried a450f once, but it was set up like a YZ, so very unridable in gnarly terrain, the suspentionsetup from the owner was also terrible, so not the best experience. He changed it back to Wr configuration, and changed the suspention-settings, and said it was like riding a new bike. Would have loved to tried it againm but unfortunatly he sold it. So please give us your input, it you end up buying one. That goes for either bike. =)