Hey Chazzy,
Welcome to the board.
First off...I too live out west and purchased a tractor to clear sage brush, do leveling, maintain my road...all things you describe....and I live a shade under 6000'.
Second....forget the post about Diesel #1 at elevation, or turbo's or whatever...diesels run fine here in the thinner air.
Third... I had shopped around for tractors for my needs. I looked at JD, Bota, Mahindra, New Holland blah blah. I also talked to my neighbors who had tractors and land like mine. What I found was that anything under a 20hp tractor will not budge the sage brush. Example...my neighbor has a Bota 18hp (forgot the number but its a B series, sub CUT). He cannot budge the sage with his....not enough weight. He has to take running starts and sometimes that won't even work. He winds up using his backhoe to rip it out bush by bush (very time consuming).
I settled on a Kioti CK25 HST with a BH and Box Scraper. The reason is that it weighed considerably more than the other brands (the thing is built like a tank), and the price was VERY right for me for a 25hp CUT (Compact Utility Tractor). I got the backhoe for clearing culverts, to do major cuts in my hillside when leveling, trenching blah blah. The box scraper I use for road maintenance and cutting fire breaks around the house.
I can tell you this...I was SOOOO happy when I got home and started cutting a trail thru the sage with no problem (no units available to test drive). My sage is a bit smaller than what you describe, but I was pretty happy with up to 3' high.
My advice, skip the BX's (too small for the job) and stick around 25-30 hp with the larger wheels. HST is fine and allows you to steer with one hand and have a cold one in the other /forums/images/graemlins/smile.gif You'll definitly could take advantage of a box scraper for your road. What you might have to do, is what I did to mine when I first moved in. It had never been scraped and had major ruts in it. I rented a larger Skip Loader and did the first time with that. I can now maintain it with the smaller tractor. I wouldn't mess with a bush hog. Sage brush is deeply rooted and thats the problem...not the height. Once cleared, it grows back at a VERY slow pace, if at all...so be carefull of clearing what you don't have to as at least the sage keeps the dust down and the dirt in place when it rains. It also keeps weeds from growing for some reason. Once removed, it will be replaced by weeds (mustard most common here).
I have attached a pic of the very first drive on my Kioti when it arrived. I rolled it right off the dealers tractor and into the sage...I didnt' stop for 2 hours until my wife yelled at me for clearing too much (dust problems)!
Good luck with your purchase, whatever you get
NevadaSmith