I believe the 511 is the largest hoe for the 6500. You can get a 509, which is a little smaller. Before you put a 511 on a 4500, make sure you have enough gpm's to run it. I know of another person who has a 4110 with a 511 hoe on it and it only produces about 7-8 gpm's and that is not enough. My dealer told me that if I was going to be running mine all day long all the time, he would put a pto pump on it.
Yes, it is a sub frame mount. It hooks up real nice. First time I put it on it took me about 10 min. It is not hard at all. What takes most of the time is taking off the top link and the stabalizer bars on the lower link arms. The are in the way of the hoe when you mount it up. Back tractor to hoe, connect two hoses, roll the hoe up into the mounting arms at the bottom then up to the top mount, drop two pins in, and off you go. Real simple and fast.
The 7k price is about right, but check to make sure that includes installation, bucket (what size), and freight. Mine was over 8k with everything done delivered to my door. I'm telling you, if you need a strong piece of equipment, that can handle about any job, you got to see this hoe mounted up on a 6500. Now all I have to do is practice so I don't make a mess of things. You can tear up some groung real fast with this thing.
If you are really interested in a hoe, let me know and I can hook you up with my dealer in Ohio. He has installed a number of these on the tractors. Do you have a kmw loader or a Great Bend? There are different mounting brackets for the different loaders on the 6500. I guess the same is true for the 4500.
Oh, and 1 more thing. Think through what size bucket to get. I got a 16" and did not make the right choice. I am going to switch it out for a 12" (smallest) and also get a 24". I am doing drainage work and don't want the trench any bigger than necessary to carry a 4" pipe. 16" too big for drainage trench and too small for clean out work around pond, ditches, etc.