Yeah its a hard one to compare, as they flex differently and also fit very differently. The 10 flex from Full tilt is around a 120 flex from salomon I would say, so about a 8 tongue should compare to the 100 flex of the spk this year.
But yeah they dont fit anything alike, so if you have been in a spk and it fitted well, its unlikely going to a boot with a 5mm smaller last will fit well. If the SPK were too wide for you they may be an option, but go to a fitter and see what he recommends, and remember a custom footbed is hugely important so put about $200 of your budget aside for that.