It's so easy for us to spend someone else's money ... but allow me to interject another thought on this.
I mow 4 acres. I started out with a smaller mower, 17hp Bolens 48" deck. It took a long long time to get the mowing chores done. It was a used mower and needed worked on much of the time, so mowing was frustrating. I traded the bolens on another used mower. A 17hp Simplicity with a 54" deck. A little better but I was soon fiinding out even when the tractor has lots of umph left in it the mower decks wore out first and could nickle and dime you to death, or simply be frustrating to keep going. Please note much of my yard is an old tomato field. Rather rough in some parts.
Next I added a used 17hp Mitsubushi to the fleet 60" deck. We mowed with two mowers and cut down mowing time considerably. Mower deck problems with the Mitsubushi were even more frustrating. It had a huge belt that drove the mower deck and again the deck was pretty much wore out. Sold the Mitsubushi and bought a new Kubota Grand L 3010 (30hp) with a 72" RFM (rear finish mower). New tractor and new mower. Ahh life was good. The Kubota would mow the majority of the acreage and my wife would mow around the house with the 17hp Simplicity which still ran okay. The Simplicity had been burning oil since I had gotten it and a couple season later it blew out the side of one of the cylinders.
DOA. I finished up the season with just the Kubota and shopped for a replacement mower. I wanted a ZTR but didn't know if I could swing it.
I ended up using the ole budget stretcher and splurged on a new commercial ZTR, Scag, with a 62 inch deck. Sweet. It is a mowing machine. I can now mow all 4 acres in less time using just the Scag than it took with both the Kubota and the Simplicity working together. Simply amazing. Kinda fun to mow with too.
Long way of saying if you can swing it, I would strongly consider going with a commercial ZTR for your 6 acres. Your mowing time will be cut considerably and the mowing chore will not take near the toll on you it would with a conventional mower.