dozers are the norm around, whether bunching for skidders, or in rare cases, forwarders. The JD 650 is the best all arounder, an arch helps but is not required. Skid as short a distance as possible to main extraction routes. A 30 yo cat or jd might do you fine, really just winching to, almost no tramming. So when you can forward, weather permitting, it may be 3 18 hr days in a row but at least you've wood out, more wood. I'd say it'd be a good step, a real good step for you.
There are a few in Southern Illinois that bunch up hitches with D4's and JD 450's and they pull about 400 board feet straight up a hill, but no more, or they are raring up in the air like a stallion, the logs are drug low with a small arch and get quite muddy.
My research had me wanting to get a JD650 with a grapple. The 750 is too big for serious mud work and the 550 is too small for serious use with a grapple.
My observations with cable skidding with a smaller dozer is simply just, acting like you are doing something in the mud, but in reality is sort of a waste of time, but everyone's level of productivity is different.
In our area the Catapillars are not the go to machine, the Deere's are easier to work on, easier on fuel and cheaper on parts.
I'm going the flotation tire route for my bottoms ground work that is always wet and muddy. I looked into those FMC?'s and they are expensive and hard to keep maintained, and they tear up a lot of ground.
I have skidded some 200-300 board feet trees backwards with my Mustang MTL20 track loader. I would spike the end of the log with one of the grapple bucket's teeth and then literally sit backwards one the loader arms cross bar and I could drive that machine backwards just as fast, as I could forwards, after a little practice, but again, it was slow enough that it just seemed like a waste of time, better off to mount good lights and work 22 hours a day when its dry, then muck around for 8 hours when its wet and slow, I've done both and 22 hours and dry is much more profitable.
Thats my take on it,
Sam