Art,
Roy is correct... but I would like to add that light duty cutters seem to take less HP to run, and medium duty take more, and heavy duty even more.... Even if they are all 5 foot units....
Not that your tractor is light on HP, but I would look into what you are cutting, and if it is not heavy brush, a light duty might go through the tall grasses easier than a Heavy Duty.....
You might get by without the FEL with a light duty. I have the deere MX5 for my 3720, and I use it on the 5303 sometimes... I like to have the FEL on it, but it is not needed.... It just feels better to me.
There are a lot of deals out there on the LX models from deere, since they are discontinued.... Some of the prices are close to TSC...