Hi, new to TractorByNet and noticed this thread...
I bought a 2013 x750 with an HC60 deck last month, trading in my 445 with a 50 in deck, so this is where my comparisons will come from. I mow 3 acres around my house. The x750 is a much better machine than the 445 and much more comfortable. I've mowed 5 times with it, so I think the infatuation stage is over, and I can say that I am still impressed with everything: the evenness of cut, operator comfort (fantastic seat) and ease of mount/dismount, fuel economy, power, and steering. I purchased it with the main intention of mowing, but I also wanted a machine that I could by implements for, such as a tiller or a front blade. Some are upset that a FEL is not an option with the redesigned frame, but it is a non-issue with me. Yes, the 445 had that capability, but I did not need it.
Maintenance is by far easier on the x750 than the 445. I love the drive over deck with auto-connect and the easy-access radiator screen. I have had the deck off three times, and the first time was frustrating. The second time better, and the third time it was done in 1 minute. The hood lifts off easily for complete access to the motor and it feels substantial. A little wobbly on the hinge when fully raised, but it is not weak. The deck leveling system is easier than the 445 because you don't have to squat or lay on your side to turn the nuts on the lift mechanism. There is an access hole through the seat pan on either side and a special wrench to turn the lift nuts. Frustration the first time, but now it is quick and easy to level the deck.
The HC60 deck mows as even as a zero turn - really impressive. I am in the process of putting together a Cyclone Rake to suck up the fall leaves, so more on that later.
In closing, I do not miss the 445 at all. Now I do not hear that sentiment from friends who had an older x7xx or the preceding x5xx series. For my situation, this was a good move.