Re: 190/55-17, Ever run one on a 954?
I found the stock 190/50 on my 929 was as stable as anything, would hold the line like rails - it has to be for the steady riders. Put a 190/55 and it made quite a difference. Ride height is noticably higher and it steers real sharp and light, got to keep the power on through the bends otherwise it feels like it's falling in, but I love it! Definitely leans more easily, I wouldn't say flighty but it's made the bike very light. No adjustments to chain or whatever needed, just adjust the chain when the tyre's fitted. My suspension is stock.
All I can say is if you can get a part worn 190/55 try it. Got pirelli supercorsa pro sc2 and can't fault them.