To me, if your dead set on getting a tractor, some of the questions you need to ask yourself is what do you want to lift with the loader, bulk bags, bales, timber etc?
if your looking at the 16acres I would go for a 70-85hp, but basic attachments could be:
Topper
roller
Harrow
Fert spreader
pallet forks
bale spike / grab
rear ballast weight
other things to think about would be a rotovator or stone burier
for 70 acres I would start looking from 100hp upwards. If your a JD fan have a look at the 5000 series M or R series they go back quite a bit (preM&R) so plenty to choose from of all hp's
its better to have a bit of power in reserve than thrash something to death, also as you get used to it you will want to get bigger implements so the size thing comes into play again, don't forget to look for 540 and 1000 rpm pto speeds something a lot of small machines don't offer. But its all physics

if you have a bigger implement it will take less time, so it depends how much you value your time?