the zk is very fast, i was looking at buying the 52/27 myself, i demoed one the other day and loved it. i feel like it was twice as fast as my 36" stander. also it DOMINATED hills, i cut hills with this mower that my 48" walk behind wouldnt do, and i did it extremely fast. make sure you do your homework though, would it really be necessary to spend $10,000 on a new mower when you already have a 48" stander? i decided not to buy one because i could get a very high quality zero turn for a lot less than the price of a new zk.
Make hay while the sun shines!