Well I've just swapped my wheels over from a set of 18's with new falken fk452's to a set of plus wheels with used toyo's (4mm) I've been quite surprised by the performance difference.
I was expecting smoother ride, which I got, but more grip? Definitely not!
As the toyo is a very popular choice I was expecting great things from them, but I've found them squirmy and screechy compared to the falkens which felt precise and planted (with no screech!)

Is this a characteristic of running smaller wheels or are toyo's just like that?

got toyos on my porto and no prob's nice feedback and good handling with them got some cheap nasty thing for my moonie.... and it wont go round a corner in the wet

Value for money there good,i used to use them a few years back.
Smaller wheels are much better on the road.

Dropping from 18 to 16 will make the car feel very different - there will be substantially more sidewall deflection on the smaller wheel, which could easily feel like less grip.

Exactly the reason I went for 17" when I had the choice of my new wheels - best of both worlds

Yeah the does feel vastly different, acceleration is noticeably more savage also, just been out for another "spirited" drive and I'm kinda getting used to it. Those new Maserati's aren't as quick as I thought they would be

Still might see if someone wants to swap thier 17" pro race 1.2's for my 18's . .

I'm not a fan of toyos.

Had some on a mondeo and, although the grip was ok, the wear rate was ridiculous.

Falkens all the way now.