Hi Grant
I have a WM250 lathe and WM16 mill. Before I purchased these, I had been considering their smaller brothers, in consideration of limited workshop space. I have never stretched the capabilities of these machines, apart from some difficulty drilling a work-piece held in an upright indexing head, when I was simply running out of height on the mill column.
I am pleased and content with my choice of machines, but also very glad that I did not buy smaller versions. I know that I do have the capability of working on larger items if necessary, and at greater speed than smaller machinery. For example, the swing on my lathe, like yours, will allow me to turn larger (but not very large!) flywheels if/when I want to make a steam or internal combustion engine.
It depends on how much room you have to place the machines, and how deep your pockets are. As you suggest, you will not know what projects will take your fancy in the future!
MT3 tooling will be more expensive than MT2, and in any case you may well find that tooling and work-holding costs will soon approach that of the machine, whichever you choose.
A larger milling table may allow room for two working set-ups on the table, or allow a set-up to be undisturbed while using the mill just for another drilling job.
This may not help you very much, but If you have room, and can afford it, the larger machine may be attractive. But as I say, I am happy with the WM16.
Martin.