2040 would be VERY unbalanced with a typical 7' mower. And HP wise, you'd be over-matched with a 7'er also. A 7' flail, and you'd need to stay in low range 1st gear in anything except mowing the lawn. I've got a 2440 and a 2640. (60 and 70HP) A 7' flail was WAY too much in heavy grass/weeds for the 2440 at any sort of reasonable ground speed, or without making multiple passes. The 2440 is quite a bit more tractor than a 2040)
I'd look at 6', medium duty cutters. A typical 6' heavy duty cutter will require a good bit of front weights. 2040's are fairly short wheel base, and typical front end weight for a tractor that size. NOT a good candidate for extreme HEAVY duty mowers.
The "theory" that a rotary mower only uses half of it's cutting width has ALMOST as much merit as the earth being flat, the moon being made of green cheese, or pigs being able to fly.....ALMOST as much....Anyone with as much as an ounce of intelligence can see right through that bogus claim.