farming full 20 acres? It might be easier to figure out how fast you want/need to get the work, and let the implements needed to make that happen drive the size of the tractor.
When looking at tractors It's easier to figure out what to buy after identifying what needs to be done, how fast it needs to be done, what implements will be needed and if there are any minimum/maximum performance or size limits that need to be considered. .....and it's better to plan ahead, because swapping out implements for a larger/smaller tractor can become far more expensive than changing tractors.