I think it depends on what you are going to use it for. I have a 60 for my BX22 it is easy to load it with too much dirt and stall the tractor. I suspect snow woould do the same (it don't snow here) I would suggest a 54 myself.
I'm very happy with a LandPride RB1560 (60") on a BX2230. Use it mostly for snow removal and leveling gravel on driveway and beach. IMO, 72" would be too big. Also, since the RB1560 is a full size Cat1 RB, you need to shorten the 3PH lift (as described elsewhere on TBN) to get more height.
In addition, I welded up some brackets and added a couple of Meyers snow plow skids. Blade height can be changed in 1/8" increments by redistributing a bunch of washers on the vertical shaft of each skid.
I have a rear blade that I have only use for snow so far and I was thinking it was 60", but I just went out and measured it and it's 72". I use it on my BX2200 and I can turn all the way around without hitting anything it's cat1 and I didn't have to do anything to get it to lift. I do have the Pats Easy Change that effectively makes the lower lift arms almost 4" longer.
On my BX23, I had a Woods RB60 (60") that worked just fine. However to make installation on the 3pt easier, I reversed the top pins so they were pointing in instead of out. Kubota claims that the BX23 has a CAT 1 hitch but the spacing seems to be a little tight.
I also have a Woods RB60 but have left the pins pointing out. I did not find this as much of an issue as toplink size- a shorter one was needed.
I have used a 72 behind my BX2200 (normally used on my 2410) but would agree that this is alot of blade for anything but light grading.
I've been using a 60" Midwest behind out BX2230 and its about perfect. I tried a 72" model but it was just a bit too much and with snow it was stalling out the BX when pushing backwards.