I have owned both,currently have a 2012 650. At 6'1" 200 lbs, either is comfortable, the wee seat is a bit lower, so I dropped the pegs using Honda GL1800 foot pegs to give my old knees a little more room. That helped. I have always put after market seats both 650's and the 1000, I found neither comfortable after 3 or 400 miles. the Suzuki Gel was good, my current 650 has the Terry Adcox rider and passenger, and they are very good. I think I spent $350 on the seat, but have put 50,000 miles on it in six years, pretty cheap by the per mile or year calculation. Most of my riding is solo, I went to Colorado and back last summer, staying on two lane blacktop wherever possible, so at those speeds, up to 70 (where legal, of course
in Nevada, Idaho, Montana, etc, the bike rides and performs beautifully. From Mt Evans to Glenwood Springs on I70, my longest freeway ride, 125 miles at 85 mph. The bike would have done that all day, no problem.
In heavy weather, or wind, cross wind can be an issue, maybe, just maybe the extra weight of the 1000 would help with that, my 1K was an 07, totaled years ago, I don't remember if it was an issue or not. My wife and I take this out on local 100 mile days, and we're both 6 foot + and, never a problem, it has a 6 speed gear box, sometimes, I'll use 4th or 5th to accelerate or climb, not a big deal. The 1K, more than enough power to haul us up any hill, or around any slow moving vehicle on a side road, that was nice, and I sometimes miss it. The lightness of the 650 is worth more to me than the extra motor. I often wish Suzuki would have made a DL800, but I do 10 day road trips on this 650 every year, commute and errand ride around town, and cannot say enough how great this little bike is for all of that.
Maybe find some local owners, and test ride ? I've let several guys ride mine, that's the best way to know.
Rider magazine a couple months ago did a comparo, 650 to 1000. They had lots of good to say about both, but they chose the 1k for suspension and power. But also said, the difference in price will put some nice accessories on the 650. Hard choice.
depends on what you want.