What I do for a unknown trailer GVW is take the axle capacity and add 10-12% of that to the total for the hitch weight...in your example that would be approximately 6200# .
My personal rule of thumb is GVW of trailer needs to be about 75% of vehicle towing capacity. If it is over that then I bring out the tables charts and calculators. FWIW I am currently towing a 31' Sovereign
where the trailer GVW is actually 97% of towing capacity of my Tow Vehicle
...but I never tow anywhere near actual gross of the trailer and I limit myself to the flat lands and it handles it just fine. There is a tow vehicle upgrade in the near future....