RM 250 experts please chime in.

To me, the biggest change will be suspension. I had an 03 that had open chamber KYB forks and the linkage was tilted the opposite way the more modern bike are. Not that it was even an issue, but going from an 01 to an 06 I don't think you'll notice much in handling..... But suspension and motor were refined

The 2006 will be light years better.

Better handling, better brakes, better suspension, better engine.

Compared to the pre 2004 models the RM is a ton better. You will love the 06. 05-08 are the best and basically the same. The Showa suspension change was a major upgrade. One of the best bikes to own in my opinion.

I have an '06, but in all honesty, if your '01 has motor mods, and suspension upgrades, I really wonder how much of an improvement you would see over a stock '06. Now, that being said, if you upgrade the '06, then yea, it will be better. I've never been a huge fan of stock Showa suspension compared to Stock KYB stuff. Any time I bought a bike that had Showa stuff, I HAD to send the suspension out for a revalve, where as the stock KYB stuff only needed a spring for my fat ass and a few adjustments on the clickers.

My previous bike before the '06 was a very well sorted 1990. Motor and suspension work. My '06 has very responsive power (and more of it, or so it would seem) where my '90 was electric smooth everywhere (nice flywheel weight and special port job) and my '90's suspension was crazy plush, never bottomed hard and was always in control (Thank you Race Tech). I've had my local suspension guy do a major tune on my '06 suspenders (had to, previous owner had it all f'd up) and it's now very nice, but not like my '90 had. What I'm getting at in all this rambling it that you make what you have your own. Almost anything tuned to personal perfection will be good, no matter the year. Well, to a point.

Might wanna grab that '06 just to have a fresh bike waiting for you when the '01 decides to surrender.

The 06 is a great bike! I liked mine, but it sat tall to me IMHO. I've always owned YZ's which to me, sit a little lower. I'm very comfortable on YZ's. Anyhow, the suspension from 03 on was better. The 06 was claimed to be the best rm250 ever built.

If your 01 has motor and suspension work, it will be as good as a 04 and up RM.

This has been my experience after riding both. I currently own a bone stock 07 250 (except for suspension, pipe and silencer) and a 2011 RMZ450. I race every weekend from April to September and I bet I race the 250 a little more than half the time. I love the RMZ so that should tell you what I think of the 250. The motor on the 250 is so electric and smooth with manageable power everywhere and the thing turns like a cat on carpet.

Sorry, but anyone that thinks the 01 Suzuki are anywhere near as an 06 must be nuts.

x2

what you will notice when you sell it and get a new yz250 is the speed and handling!!

I like having both also. They compliment each other. Most of the time I use the RMZ for sight laps while the track is wet. Then most of the time I end up putting more seat time on my '05 rm 250.
Revalve, v-3 reeds. PC pipe and a 10oz ffw to smooth out the suspension on braking/ acceleration bumps. Lessens wheel-spin also!

Plus it adds aggressiveness into my cornering w/ choosing inside lines.

I would love to get another RM250, that bike handled like none other. Dove into corners so hard, but my 2002 was absolutely clapped after a year. Pegs saggin, frame stretched, clapped. Makes me nervous to get another one.

I've had an 02 and I currently have an 06, both were stock when I got them and right off the bat the 06 blows the 02 out of the water in the suspension and motor categories, got the 02 suspension done by race tech but I never felt as comfortable on it as I do on my 06.

Might wanna grab that '06 just to have a fresh bike waiting for you when the '01 decides to surrender.

I think that's good advice right there. If you can afford it, buy the 06. Once the 01 is worn out, start riding the 06. Most of us do not need the latest bikes to have fun on.

If you really like your 01, it's reliable, and you've got money into it, go buy a set of Showa Twin Chamber forks for it. Better yet, buy the whole font end off a blown up F-bomb. (I know hard to believe, but they ARE out there.) I bought a whole bike, plus an extra front end, from a 450 Zook.