I've got the 553 loader. I believe you can get larger loaders on this model, but I really see no need. I've spent quite a bit of time on backhoes and have gotten used to the capacity and speed of their loaders. It's hard to match that with a farm tractor, and I was very skeptical when I first picked up this tractor. I've been very pleasantly surprised. It's definitely not as fast as a backhoe loader, but I've used it quite a bit and have yet to come close to it's limit. So far, I regularly move around 1600 # bales of hay. I've graveled about 1500 lf of driveway with crushed concrete and brick mix and moved various piles of dirt, implements, etc. It hasn't yet hesitated, nor even slowed down in the slightest. I've been surprised that even with a full bucket of gravel or a bale of hay, I don't even need to throttle up. It lifts everything at idle engine speed. My tractor, with loaded tires and the loader attached weighs close to 10,000 #. In my experience, it has been very stable, no matter what I've got on the loader. Even without a 3ph implement to offset the weight, it seems stable. In fact, until you mentioned the weight in your post, I hadn't even thought about being underweight while using the loader. I've yet to take the loader off. I haven't really found a need. I remove the bucket fairly often to use the spear, but I haven't taken the loader itself off. I really can't see any reason that I ever will. It doesn't seem to be in the way at all.
As for the turbocharged 4 cyl, I certainly haven't wished for more power yet either. I bought a little more tractor than I needed, though just for that reason. I didn't ever want to wish for more power. I've not used a 6 cyl, so I cannot give a comparison, though.
I have used some ground engaging equipment. I use a disc harrow often, although a smaller one (6'). You literally can't even tell it's there. The only other ground engaging equipment I've used is a subsoiler and a box blade. They weren't an issue at all.
The steering wheel is personal preference, obviously, but it surprises me that anyone would think it's too close. Being adjustable, it can either be in your lap or in the vertical position, which I find to be a stretch to reach (and I'm 6' 220#). If it would help you, I can take a picture of my leg room with the wheel in the vertical position and another with it where I use it. That way you could better picture how much room there is. Just let me know if that would be helpful and I'll post it in this thread.
All in all, for the work that you are describing, I wouldn't give second thought to the weight of the tractor, nor the capacity of the loader. I do the same types of jobs and it performs well. The only limitation is the maneuverability due to size, but you should be used to that with your 2950.
I have no idea about the availability of a buddy seat, but I don't think there is really enough room for it in this cab. I sometimes carry my 90# lab with me, but it is cramped. My wife has ridden short distances sitting on the wheel well and it is very cramped. I imagine a buddy seat would be very uncomfortable. Edit: just to clarify, I think there is plenty of room in the cab for me and I don't feel cramped at all when its just me working, but with someone else it definitely gets tight.
Good luck with your search.