I have a 2004 mxzx 740 (440 chassis) with the SMALL 440 cooler. I"M runing 96 studs...I also have ice scratchers. With the ice scratchers not deployed, i am running mid-way on my temp gauge. When my scratchers are down, the needle doesn't even go over "C" (cold). Infact, i even thought my sendor took a ####, since it wasn't hardly moving. SO, I picked the scrathers up and the needle rose, so I knew the scratcher really kept the sled that cool! The ice scratchers work AWESOME.
By the way, for 121'', you can only get the HOLZ scratchers that mount to the bottom of your runnig boards. The rail mounted ones are for 136'' +.
IMHO, if you dont ride ice too much, and want to stay cool all the time, with or WITHOUT a big lug track, ice scratchers are the way to go.