I thought Morton was wood framed, not steel framed? But to the question, you get what you pay for. Compare the gauge of the purlins, girts, sheeting, and main frame rafters. The reason that I mention gauge comparisons is that, as an example, the common 'Z' purlin can be purchased in many different gauges. A quick search showed 12, 14, and 16 gauge are all available.

Compare the spacing of the purlins and the girts. What is the spacing on the main frame rafters. A lot depends on how you are going to use it. Cold storage? Heated storage? Heated workshop? Pay attention to insulation options and interior finishing options. If heated, decide what kind of heat you want, I have floor heat and love it. I note you mention a 5:12 pitch, most true steel buildings are much flatter, around 1:12.

Around here Varco-Pruden and Behlen are common. I have a 50' X 75' Behlen with 25' main frame rafter spacing, 5' purlin spacing, with one wall girt at about 8'. Wall height at the side walls is 12'. If I had bought it new I would have gone with the thicker steel door jambs (I have the 14 gauge) as I have problems maintaining alignment on my 10' X 10' overhead doors. I would have also gone with the thicker wall girts simply because when you start hanging cabinets and other things on the wall you have more to screw in to.

I'm no expert and these are my opinions, nothing more.