Replying to Big guy 1260 or 4frnt stl

I'm a bigger guy 6ft 220 and am currently ridding the yellow 1260's with the nija's on them. They are 177. I'm looking to get last years 4frnt stl and was wondering if they are any stiffer than my lines. I ski in Indiana so all i have is the park, groomers, and ice. I know these are really soft skis but i had no problem with my 1260's except if i was straightlining a hill and making a hard carve then they were a little squirley. My lines aren't center mounted but they are close. I probally spend 60% park 40% all mt. Would the Stl's be any stiffer and what size 183 or 177.