I'm the one looking to get back into the 2320/2520/2720 range tractors, having traded my 2320 down for a 2305. "Penny wise and pound foolish" couldn't be a more appropriate statement for my mistake. And to be clear, I'm quite aware that I'm considering the upgrade more out of "want" than "need." I'm simply not satisfied with the tractor I now have and its limitations have only become apparent over the course of 6 months of ownership. It's the perfect tractor for a lot of people - I'm now aware (too late) that the 2320-2720 range tractors are perfect for me.
JJKJ -
As you say, you don't want to do as I've done. i.e. take a 30 day test drive and realize the tractor you've chosen isn't right for your property. So let me chime in about my actual experience with my 2320. My ONLY complaint of consequence with that tractor was the 2-range hydro. High was too high. Low too low. But in many ways that was my impression, rather than necessarily reality - if I stomped on the hydro when in high, the tractor eventually moved along just fine. But boy did it make a whining racket! On a slope in high range, the tractor SOUNDED like it was straining and yes, it took a lot of effort to get moving. But, it did move. Sounds to me like you've had this experience with your X500, but perhaps to a lesser degree.
So, my guess is the 2520 is better and the 2720 is best with regard to straining. I think for you it probably comes down to trying each one out or the two that you are looking at - which may necessitate a trip to a distant dealership that actually has both in stock. And a hill to try them on. I would suggest spending some time on them, too, using your ears - and don't let a salesperson make you feel rushed.
The 2320 does not have direct injection, but I never had trouble starting it in severe cold weather with the glow plugs. i.e. -15 degrees. It would spit black smoke for a while and sound god-awful (loud! and pingy) compared to staring in the warm summer months. But it would start and settle into itself (same is true of the 2305 I have now) just fine. So, for me the direct injection is more gravy than necessity.
As it stands, I'm still in the contemplation mode. I'm waiting for a day that will allow me to compare several tractors on the same day - which means a weekday, as many local dealers are only open for a few hours on Saturdays. Rarely do I have a weekday off. So, I'm a ways out from doing anything. My point in mentioning this is, I'm not adhered to any one brand. I am intrigued by the Kubota
B2620 and
B2920 models, as they have a couple of features I think are valuable - the 3-range hydro, hydraulic couplings that don't leave lines hanging just off the ground and are easier to access and a retractable seatbelt to mention a few. Not that the 2320/2520/2720 don't have their own benefits - i.e. position control, one-piece engine cover, etc. It's just a matter of getting on them and trying them out back-to-back so there's actual comparison, rather than just looking at specs on a page.
Good luck. Thanks for posting this thread, as my mind's hung-up just like your's with regard to the hydro comparison of 2320 and 2520. Hopefully someone has an anecdote that clears it up for you.