Price is high and the mpg claims are bogus. I had an 07 600HO SDI in a shorty, it's a great engine, but doesn't get that kind of mileage, especially pulling a renny. Unless the owner was an old lady who only went 20 mph back and forth to church on Sundays?
I have the 6.9's on my renny and love them but I think for your riding you might want to go with the DS's. If you go with the 6.9's then swap skis (l &r) so that the outer keel ends up on the inside. This helps lay over the sled easier.
I went with what many others in this forum were doing a couple years ago and glad I did. I put pilot 6.9's on my 11 gade and they balance out the machine perfectly, I can only assume the wider DS would do the same. In powder and loose stuff the skis are an absolute dream. I put 7" shapers on and adjusted the ski pressure and the machine is perfect in the high speed sweeps like you find on rail beds. I thought the sacrifice would be handling in the tight twisties but I was pleasantly surprised how well the machine turned without wrastling it and having it push in every turn. Don't just change the ski and expect miracles, put on quality runners with big bite and adjust your ski pressure to your liking, how much you stud your track will have an effect too..