I have read many articles where the 450i will outrun a 500 UXV except for top end speed, most claim in a drag race the 450i pulls away from a 500 up to 35+ mph in fact I remember seeing a video on that. Now 27" tires may be a bit much....can't say for sure but they will change your gearing especially on the hill climbs that you seem worried about. I am moving to 26 when I replace my tires, but 27's I don't know about those...I also like tight technical trails, not a speed demon and the 450i is great for that, just what it is designed for.