You may want to try the John Deere MX series as they are billed as the medium duty rotary mowers. As the MX series is the medium duty variety, there are a few more of them around (both new and used) as the price isn't as steep as the heavier series you mention. For the number of acres you mention, I feel the MX series is more than enough to get the job done. I was looking a few years ago and decided on an MX5. I pull it with a 50 hp JD2020 tractor and it works great. I mow about 20 acres with it, so it isn't the fastest way to mow, but it has cut through everything I have asked it to go through. I paid $1700 for the MX5 new, so you should be able to get a good used one for a lot less than that.