Someone asked me over PM to give my take on my 690 Duke vs my old 950SM. I figured it's probably better to put it here for posterity than hidden away in a PM.
To be honest, it's almost exactly what you'd expect the differences to be between a big torquey v-twin, and a welter-weight single. If you want the short version, the 950SM is a better all-around street bike while the 690 Duke is more fun and focused. They're both great bikes, I'd take either one any day, they're just different. For the long version, keep reading...
First of all a little background-I had both bikes for about a about a year. I had the 950 last year, sold it last fall and bought the 690 in late spring of this year. I put 13k or so on the 950 and about 6k on the 690. They are my third and fourth motorcycles, respectively. While I don't claim to be an expert by any stretch of the imagination, I'm a fast intermediate\slow advanced group rider depending on which track day org you pick. Lastly, I didn't really mess with either bike's suspension and didn't do any serious mods.
Now I am a little biased in that I love a good v-twin, but I miss the 950's power. It had great torque, a power band as wide as the titanic, you could lug it around, and you have serious forward motion when you want it. Plus, being able to power wheelie off rollers at 70mph+ with just throttle is nothing but fun. It's also smoother, more power is obviously better in traffic, and it doesn't care if you throw another person and some luggage on the back. The 690 is definitely not anemic, it's head and shoulders above my DRZ-450, but it's not winning many drag races either. While it does have pretty good torque, the power band is surprisingly narrow and it shudders below 4k. It's not as buzzy as you'd think on the highway. You can still power the front end up in third if you chop it and give it a little bounce, but it's more work. That said, it's pretty fun to wring the crap out of a bike as opposed to always feeling limited by wreckless driving tickets a second after you open the throttle. You're definitely shifting a lot more but, again, it's fun.
The 950's monoblocs are the best brakes I've ridden to date. Great feel, great power, one-finger stoppies. The 690's are really good, better than most other bikes I've ridden, but I could stand for a little more power for less lever input. Just a limitation of one caliper vs. two. That said, the 690 has a slipper clutch which is on point at the track under hard braking. While I like the brakes on the 950 more, I would guess that I could stop faster on the 690, mainly due to weight.
It really depends on what you're looking for. The 950 has more travel and is definitely the squishier of the two. Combine that with a generally bigger bike, and it's a more comfortable bike. If I wanted to go to Kentucky for the weekend and I had the choice, there would be no question that the 950 is the way to go. Beyond that, the weight of the 690 and the stiffer suspension make it a much better handling bike in terms of all out performance. On the 950, I would brush a puck every now and then, but most of the time my toe would hit the ground first. On the 690, I can get knee down on almost every turn on the track, from 20mph to 90mph. The 690 is also, surprisingly, the more stable of the two, with it's super long wheelbase it's got much more of a "carving" feel to it. It's much more forgiving and when it starts losing traction, it happens slowly and is very easy to control. The 690 gives meaning to the word "railing." On a small track or deal's gap, I can't think of many better bikes.
I'm not a big off-road guy and obviously both bikes are not off-road bikes with a 17" front, but as long as you don't have a clearance issue (which often you do on the Duke with the underbody exhaust), I'd still take the 690 with less travel just due to the weight. You're not taking either seriously off-road, but they both do fine on milder stuff. The one respect that the 950 does trump the 690 in the handling department is two-up. It's just more stable and less sensitive to adding weight.
As I eluded to, the 950 is a lot better two-up or touring for a variety of reasons, mainly just because it's bigger.
They're both KTM's so neither has been perfectly reliable. I blew out the clutch slave cylinder on both of them at the track. The 950 needed the water pump shaft seal done and the 690 needed a fuel pump so the 690 may be slightly better there. I'm not a carb guy, so I love the FI on the Duke. Fiddling with carbs sucks.
The 690 is cheaper to run just because it's smaller. Less oil and I get 60mpg+ commuting as opposed to the low 40s (mid to low 30's wide open) I got on 950.
They both get a high hooligan rating.
Like I said, they're both great bikes, it just depends on what you're looking for. I bought the 950 because my then-fiance, now-wife was doing medical rotations all over the region and I knew I'd be riding a lot but I still wanted to have fun. Then I started doing track days and realized I needed something a little more focused (and a little more forgiving) that would let me get fast. On the 950, I almost high-sided the sh*t out of that thing on my first track day. On the 690, I went from beginner to advanced group in 4 track days with not a single pucker moment.
To me, the 950 is an epic hooligan touring bike that still gets down like a sport bike.
The 690, on the other hand, is a very focused, handling superstar that will embarrass sport bikes in the bends.