I feel that I have an experienced, yet unbiased, opinion on this. I have owned a 97 620 Duke and an 06 950 SM. I own neither now.
The 620 was a great play bike, but just didn't have the legs to be any kind of a bike to take a real ride on. And those earlier LC4 motors as used in this Duke, vibrated quite a bit.
If I were told I could re-own one of these bikes today I would buy the 950SM. I wouldn't even look for/at a Duke. Hands down, no question. Shorter around ton rides or longer trips, the 950 was better in all regards.
07 Yamaha R6
07 KTM 950 Super Enduro
04 KTM 250exc- plated two-stroke
01 Kawasaki KE100
74 Honda MR50