i have one of their reflective sheets and its small, which is 4'3" and i use it on my 16.2, it fits perfectly, alittle short but that its how i prefer them so as not to have too much flapping around. maybe if you wanted one to completely cover them go for medium
I have a Rhino competition sheet, .. it is a medium and fits mine well (def not too long) - he is 16.1 Trak, stable and turn out size rugs for him are 6ft 6" - if the gold stripe exercise is the same material as the gold stripe fleece rug then it should not flap
My boy is a big 16.2 but not a massive bottom. I bought one a couple of years ago but it was far too big so gave it to my friend who has a 16.1 ID X with a lurvly big behind and it fits him. I think it was a large - I should probably check. He does have 6ft6 rugs but I like his rugs to have plenty of room so I think I will go with the small cause I just want it to sit a couple of inches up from his tail. Thanks for all your help guys