Power is power within reason - old or new. Should not see a difference with an older healthy engine versus new. The main difference will be in weight and stability. Typically the older tractors are heavier and, thus, more stable.
That makes sense. For a size comparison all I have is my 8N. I know there are times when I would like to mow in a higher gear or use a fuller pass with my 5ft brush hog then it will do. Looking at tractor data it looks like the 1620 and the 8N are pretty similar HP wise and also weight. My 8N runs very nicely so I think it's running as close to designed as a 60+ year old tractor can. But I have nothing in the way of comparison or experience. Should I assume that the 1620 (and for that matter) the new 25HP Kubota/LS would be similar and start out by shopping bigger? Or can I just assume my 8n isn't running at full output anymore? I cut everything down in the fall so even if a dealer would let me demo I won't have and decent height brome grass to cut until middle-late May (normally) for a test. I've read on the forum to go one size bigger than you think you need but not sure 8N is a good baseline. I like the price, and if I understand right 25hp gets under tier 4 in the new stuff, but don't want to go to small. But I know I've read posts were people were going all sorts of tasks (mostly with timber) on bigger acreages and they were shopping in this range. Maybe wait for something older with more HP???