I'd look at the Hp requirements for the disk. You don't say what width you need but I think that the disk mowers take a fair bit of power to run. They're certainly nicer and I've seen them rated up to 12 mph on tractor models and higher on self propelled models. Unless your field is nice and smooth you probably won't be able to run anywhere near what the disk mower is rated for so you may be able to get by with a little less than the manufacturer suggests.
Sickle bars are way more dangerous. I'd go with a disk. I'm assuming you are wanting one for haying. How about a combination to buy one less piece of equipment?
We own a Wild rice farm in northern MN.
Mostly looking to cut grassed along dikes and ditches surrounding the paddies.
Not much haying so speed not too much a concern.
I do like the idea of vertical cutting with sickle bar for small brush overhanging a trail.
Check out the Ibex disc mowers. They are sized to work with the compact tractors and easier to operate than sickle bars, and less likely to get jammed up or damaged from hidden obstacles.
I believe a TS53 would be the right size for that tractor.