I too had ridden an older Mach I. I found some of the same characteristics in a Connelly Concept. I agree with yellow, try adjusting fin and moving boots before you give up on the Vengeance. If you are still not happy, try to demo as many skis as possible. I ended up with
an '05 Hook because I found a screaming deal on eBay. It has turned out to be a great ski for me. I'm 6'3" and 230 so I went for a 70". I'm still an intermediate free-skier so the extra length helps. I too find that 36 MPH is my sweet spot. The extra speed covers up my poor technique . Good luck, and let us know how it turns out.

Dave