If you plan to buy the "DA" model tractor with a hydrostatic transmssion, don't bother with the TC45DA. The dealer gave you good advice. The only thing where you can even remotely see a difference on that tractor is in PTO HP. I guess if you wanted the maximum width rotary cutter, you might get one on the TC45DA that's a foot wider than the TC40DA. That's considering you use the formula of 5 hp per foot. In all honesty, I don't think you will want to go above 7' on either tractor. An 8' wide cutter is pretty darn large unless you have a very open field.
The hydrostatic transmissions on both those tractors uses the same pressure relief valve, so the TC45DA can't pull anymore than the TC40DA. Also, the hydraulic pump pressure is the same, so the 3PH and the loader have exactly the same specs on both tractors.
I guess an argument could be made by someone buying the gear tractor that the extra 5 hp was worth the money, but I don't think that's true for the hydro. Save your money for other "goodies." This is coming from a TC45D owner. If I had known what I know now, I'd be driving a TC40D instead. /forums/images/graemlins/smirk.gif