Which of those units do you find comes closer to the amp loaded down into a capture? Also do you find much difference in a good amp capture and the amp loaded down?
What do you mean by "loaded down"? Are you referring to an impedance mismatch or capturing the amp into a reactive load and not the cab, in other words a DI capture?
Depending on the amp, the load can have a significant impact on the tone, so doing side by side tests, I used the Suhr RL built in load to make the captures and then played the amp through the Suhr into a Mosvalve power amp and then into the speaker cab. The captures were played back through the same Mosvalve amp and same speaker cab. We tested a BF Super, a moded SF Twin, and a 50 watt 1968 plexi clone. If doing it again, I would definitely use a wider amp selection, but just three was pretty time consuming.
When I make captures for normal use, I stick the Suhr in between the amp and cab so that the internal load is bypassed and the amp sees the actual cab's impedance curve. All the difference is in the amp reacting to the load, the capture devices handle them exactly the same.
For the amps I have tested, and again I am NOT a high gain player, NAM (tested later) Tonex and QC are so darn close to each other and the amp it is hard to impossible to tell them apart most of time. Kemper was often easy for me to spot. I think Tonex handled wider swings in guitar volume output better than QC, tested with a Strat with the Fender mid boost circuit installed. I did not test NAM to the same extent, and not at the same time.
All in all, I would have a very hard time picking out Tonex from NAM from QC or from the real amp for these tones. Tone would not be a consideration for which one I would use. Tonex kills NAM for me simply because of the hardware options. Tonex beats QC for me because I am using it as a substitute for a real amp and all the effects are usually coming from a pedal board. If I wanted an all in one solution, Kemper or QC would have beaten NAM and Tonex, but in the future I am guessing it will be Helix Stadium for my inevitable next all in one digital rig.
Separately, I did some much less rigorous comparison of the capture plus York IR into a CLR against the Twin with D120's side by side. They were closer than I expected but still easy to tell the "amp in the room" from the IR into "FRFR". This is a pretty imperfect test though because even though York's IR was captured with a Twin as the cab, it was a different cab, different (old) speakers, and then there is the mic'ed cab vs the real cab issue.
It may seem weird, but I have never done full captures with a mic in front of the cab. I prefer to be able to change speakers/IR's as a tone shaping tool, my mic collection is pitiful, and I am not particularly skilled at micing a cab. So, I only use DI captures that I made or from Amalgam, and then I play through real cabs, or if I want to use headphones or an "FRFR" (very rare) I add IR's from various sources.