I was in your boat and compared some versions like you have suggested.
From my research:
Briggs Pro Turf - at best, high end residential motor.
Kohler Commander - good motor, but uses (I believe - as I was considering a 223 version), a "mule drive" set up that tends to "sap" power due to the way the engine power-to-deck is routedl.
IMHO - If you move up in cost ($7.5-8k) you can get a MUCH better machine. The Grasshopper 223-52 was on my short list - but the Gravely 152 and Scag Tiger Cat 52 were there too. In the end, I ended up purchasing a Gravely Pro Turn XDZ 252 (w/ 23.5 Kawi) for around $8k. IMO - a much better machine than the GH. Huge transmission and frame, etc. etch. I purchased with 1/2 down through Sheffield at 0%/48 months (Sheffield financing is available for Grasshopper, Gravely, Scag, etc.) Heck of a deal.
If you are interested, here is my research...