you can basically go as fast as road conditions will allow in 4hi, and no im not saying hop on the freeway and do 75mph but think dakar rally or baja. if your on dry or wet roads where chances of slippiing is virtually nonexistant, running in 4wd will just tear up your running gear. in my case, thats why im constantly in and out of 4hi while driving around town and even on the highway (without stopping). also, where your traction control is on the spectrum from locked up to open diffs would be a huge factor in this. the more traction control i have, the more leary i would be of going into 4hi for a dusting of the white stuff.