I would compare that engine to the D6C 10K series just prior to the change to 3306 and it is rated at 125 hp
Just for comparison the 17R SA is rated at165hp.
For the 8M4948
Forward: 1st=1.8mph, 2nd=2.5, 3rd=3.0, 4th=3.6, 5th=6.0
Reverse: 1st=2.3, 2nd=3.1, 3rd=3.8, 4th=4.4

bursitus I understand your wanting the most for your efforts. But my experience has been until you really use it hard to tell just how one will preform. I have 4 9u's here I have run, pulling the same tillage equipment, there is a difference. But until you run the "better" ones you don't know it.

I farmed stepper than sidehill combines will level up on. I do not advocate working that up and down. But when they put trees on it that need tillage to save moisture ( another discussion about farming practices, it does make a difference in my conditions ) you do what you need to do. Traction more than engine power has always been the limiting factor. For the traction issue I have both a 12 foot and 18 foot heavy offset discs. Yes I can spin out even with the 12 foot.

So if you do not already have the tillage tools you wish to use, forget the engine horse power . Look for the best condition of the big things like undercarriage, and final drives as they need pullers to take apart that most don't have. Yes engines and transmissions are important but the special tools are easier to find for that work than the big pullers used on final drives. So the parts needing special tooling limits choices of who can fix it for you.

But as tuff and long lasting as Cat's are it is hard to tell how good the insides are of 40 to 70 year old tractor. So history if you can get it does matter. But mine have all been "pigs in poke", with one finding thing after it did not matter ( all good).

I hope you end up with a Cat that meets your needs and WANTS. I always wish I had a little more than what ever I am running. So I do advocate for bigger than you think you may need.

Thank You All for your insights.