What length is your trailer? Since I don't know this, and going by the spec sheet from Bigtex, lets assume its 18 feet. With a GVWR of 5000#, you have to consider both your load and the weight of the trailer. The 18 foot 50LA weights 1,570#. That leaves 3430# for payload, under the best conditions if you want to absolutely MAX out your available GVWR. That doesn't get you a very large skid steer. I would be concerned about the ramp gate, but even if it is beefed up (also, adding weight) then you have to consider trailer frame, axles, wheel bearings, tires, springs, wheels, etc. Unless you're getting the smallest skid steer they offer, I think you need to upgrade trailers. I would recommend at least 10,000# GVWR, but depending on the size of your equipment, you might consider 12,000# or 14,000#.
Edit: Just noticed you're looking at 4000-5500 Lb range skid steer. In that case, a 10,000# trailer would get it, but if you ever considered going bigger, I would up the trailer GVWR more as well.