I've got an 08 D-7 coming off an 07 summit x.
Yes I'm down on power,but for me,the sled is so much more reliable.I've re geared it this season to 19/42 from the stock 20/41.
The X would eat belt's every 400 miles or so even with venting and Doo's clutching updates.The final for me was when the ECU died weeks out of warranty.Still on my second belt on my D-7 so far in 1900 plus miles.
Xtreme Performance Center who I bought my sled from,here in Colorado,had high altitude dyno reports showing the 08 D-8's only making 4 more peak HP than the 700's.In the mid range there was more of a difference,but the 700's haven't had the reliability problems of the 8's.Unfortunately Xtreme no longer with us due to the economy
Pete
Same story as me... I'm VERY happy with my choice!
