I can go as fast or faster on my ZTR (10mph) as I can mow with the tractor because the ground is so rough, the tractor will beat you to death. Due to lots of trees, I have to circle around a lot to get even close to mowing all the weeds which is not needed with the ztr and I think I have less overlap using the ztr mower. I get a cleaner cut, lower cut and same or better mowing time.That's interesting that you can mow so much faster with "only" a 52'' deck compared to your tractor. That size would work a lot better in my yard than the 60''+ I was thinking I would need get to make up any ground on the speed of a modern tractor/bush hog.
I am surprised that you are being told to skip the loader. I strongly disagree. I use a loader for driveway maintenance, moving bark dust, cleaning up after weeding, lifting anything heavy I get in the bucket or get a chain on. My wife has even lifted me up to clean gutters (single story house). You get more creative the more you use it. Once in a while in tight quarters around trees it might get in the way a little if you are mowing with it. And don't forget it helps a lot with snow. If you are buying a late model CUT they are quick attach so take about 5 minutes to take off and 10 minutes to put back on if you don't do it often. Faster if you do it all the time. To me you loose at least 25% of the usability of the tractor without the loader.
I really didn't think I would be using it much, however, I never take it off either of my tractors now. They are so handy to have and you never know when you may need to lift something.