I just bought a Ferris 61" with the BS Vanguard 26 hp. After years and years of looking and going through the rainbow of colors and types, I found rapture.
I know you are looking for a 48, but with what I found in this machine, you might include Ferris in your search since you are looking for a long term investment, if smooth ride is at the top of your list along with long term reliability and performance. Really a well engineered, well built machine.
The 44" Hustler Fastrak ZT with an 18 Honda has been a real nice, trouble free machine since purchasing in '05 and it too is well built, have only replaced spark plugs and tires in that time, but will not handle rough terrain like the Ferris. It's currently dedicated to lawn vac service.
The Husqvarna 46 big box purchase (about a 2007 year model) that had the Kohler Courage 20 hp single....it's in the trash with a BS 20 V twin replacement and ATV tires....it mows my pond banks and other structures in the 20-30 degree slope range. Had a crack develop in the deck to mounting bracket this year I had to weld up. But it is a twin blade and really sweeps the wet grass out without clogging which I really like.
The JD L110 (about a 2000 year model) has been converted to a "Gator" with a new BS V twin 18 and ATV tires. It was trouble free (except for one instance of my abusing...see comment below) and a big box purchase. It served well over the years with little to no upkeep.
The DR 52" Pro Z has provided excellent service since '05 too with no repairs required. My main dislike with it is the fabricated deck clogs and doesn't sweep clippings out like the Ferris which helps to cause the clogging problem. Deciding now what I will do with it as the Ferris is it's replacement due to soft ride and superior non-clogging deck performance.
The Scotts 42, about a '95 purchase, with it's 15.5 hp Kohler single has been highly modified to now run my 16 gpm log splitter.
So there are a few hydrostatic drive (zero hydro problems with any of them but the L110 and I caused the problem and was able to fix it with parts from Tough Torque the mfgr) inputs for you from my corral.