My wife and I both got '15 690's in late Jan and early March 15. One came with a 130/80-18 rear tire and one came with a 140/80-18. Go figure......I don't think the 140 versus 130 really makes a big difference.
I do like the stock MT-21 tires. Pretty good trade off between dirt and asphalt. I'll be changing the rears here soon at about 2500 miles, going to use the same MT-21 tire. I've used the Dunlop 606 on dual sports before. To be honest, I'm kind of afraid of changing a 606 on a cold day on the trail. I've run 606's on a Honda BRP and a Husky 511 - The Husky will never see 606's again - I'll change tires more often with the MT-21 - they are also much cheaper than the 606. Don't get me wrong, the 606 has been a great tire - no flats to date and no issues whatsoever - I just don't want to deal with it on the trail/fire road/highway - you might have no problem, but I know it is difficult for me.
Note: In cold temps when I change the 606's out at home, I put a heat pad in an emergency blanket with the tire/tire & rim - the aluminized ones - and get the tire warm - makes the job a whole lot easier. I've never had to change or put a new tube in a 606 on the trail in cold weather - scares me even thinking about it.......That tire sidewall would be rock hard!
Good luck!