Generally I think it's best to stick to whatever the manufacturer fits in the first place.
Rim size is not everything either, modern supersports racers are now almost all using 190's on 5.5 inch rims. My race bike had a 160 wet fitted to a 5.5 inch rim, so all is not as simple as you may at first think.
As for BT020's, Gods own tyre that. It's so easy to get carried away into thinking you really need the latest, stickiest race rubber to go fast but you patently do not. (Ably demonstrated by our happy desmoduers I think) As a standard road tyre on a road bike the 020 is hard to beat, and phenominal in the wet. A great combination with the 010 on the front for a sports bike.
I would suggest that turn in speed is more of an issue between different makes of tyre than the difference in size between 180 and 190, an interesting point with the 208RR which is very pointy, and the 014 which is not.
At the end of the day, the point of the 190 tyre is side grip, that's why they are used instead of the 180, and thats why most all the superbikes are now on 200 section tyres.
For road riding it makes bog all difference unless you are a nutcase anyway!