V-6 Colorado - not much guts. With your equipment and to allow some growth I would not go over 6x12. I would not even consider an enclosed pulled by a Colorado, you'd better go open utility. I pull a 7x14 enclosed with my 4.7 V8 Dakota and it does alright, except in a strong headwind/high temperature day it struggles just a bit I have to take my time. Just an FYI.
7x14 Stealth SE Enclosed with 48" side ramp
2013 Gravely Pro Turn 260 with Kohler 26.5 EFI
08 Toro Z400 48" deck, 21HP Kaw with EZ Vac twin bag
09 Exmark Turf Tracer HP 36"
21" Toro SR4 Super Recycler
Stihl KM90 Kombi w/ straight shaft trimmer & tiller heads
2 Husqvarna 125B Blowers
Turfco XT5 Aerator
Turfco LS-22 Overseeder
EcoLawn 200 Applicator
I can do all things through Him who gives me strength.