IMO, life is too short to ride tires like Gatorskins... or Marathons. They give up ride quality in exchange for puncture-resistance. I don't know what tires you're coming from, but unless they were something like Duranos, you're going to notice the stiffness and sluggishness. I'd rather patch a tube than ride a rock hard tire. But I'd rather spend a little more to not have to do either.

I pay the money and spend the time to run tubeless so I don't have to run heavy, stiff, puncture-resistant tires. You have to give up something to get that flat-resistance-- there's weight, there's rolling resistance, there's suppleness and ride quality-- I choose to give up money.

Short answer: you won't notice much difference between the Marathon and the Gatorskin unless the ground is wet. Gatorskins are like ice-on-ice in the rain.