Many dealers will let you try out equipment on your own property before you buy. I would ask, and make this an important part of your decision.
I am a little puzzled at your difficulties running a 5' cutter going up "Small hills" with a 44pto hp tractor. I wonder if your pto hp is a lot less than 44, or if your small hills would look like mountains to me. I run a 6' cutter on flat ground with 47 pto hp and have about double the hp I need. I can't imagine my tractor would bog down running the 6' cutter going up any hill that would not cause me to roll end over end.
I didn't originally notice the size land you're working on. While HST is not generally good for hay work, 5 acres is a pretty small plot and I'll bet that the
L5740, or a JD 4720, would work just fine. I would also consider Kubota's
L5040 which is available with their GST, which is a true powershift - actual metal gears, but no clutch-pushing required. It is rated for 44 pto hp, which is the same as what your current tractor is apparently rated for. I think any of the utility machines you're looking at would be quite large for haying 5 acres and mowing another couple acres. Doesn't mean they are wrong for you, but certainly are larger than I would usually think of for those tasks.
One user on here - I think Greyfields - does his own hay work with I think a JD 4320, and he's doing round bales (albeit small ones, 4x4 I think). Again, I would go utility for significant hay work, but for your purposes the CUT might be a reasonable choice.