I have a TC24D with a 5' blade and I've stopped my tractor dead in its tracks when I've grabbed too many granite cobble stones.
I've also stopped it dead when I grabbed too much heavy clay.
Last week I was clearing some snow, I had the blade angled to the right about 30 degrees, it was also offset about 6" to the right so I could push the snow over. I was in 4" of heavy wet snow that was on top of a slush-ice base. The tractor blade did a great job for most of the work. I was PULLING the snow and I did notice that the blade would force the whole tractor to the left, that was probably because the tractor did NOT have chains on it and was driving on the snow/slush. It did bog down a few times when the snow got deep at the end of the driveway and even in low gear would not move.
By the way, I have about 100# of weight on the front of my tractor to hold down the front end. (EZ Weights in the front wheels)
I'd say the 5' blade is a good size for the TC24 about 90% of the time.
The 7' blade will probably move loose stuff and light stuff, but I think it would be much more like a boat anchor and just stop you dead in your tracks if you tried to do any heavy work.