I don't think there's room to lower the forks in the triple clamps because of how the handlebars basically bolt on over the top of them. Plus, a 180/55 is probably going to be very close to the same height as the 190/50 so it's not going to raise or lower the rear much or affect the speedo much. Most people are talking about a 190/50 vs a 190/55. The 190/55 IS taller than the stock tire. So I'm sure raising the rear is part of the handling difference. However, the tire also has a "sharper" profile which makes it fall into corners quicker. And the affect on the speedo is a positive one because it corrects for almost all of the factory speedo error and makes it more accurate.
There is over 1 full inch of room before the top of the forks would hit the handlebars (more with risers) I've lowered mine and I've checked the clearance. All bikes are designed to move the forks up and down slightly in the clamps or they would just mount them solid to the clamps.
This also puts your feet 1/4 inch closer to the ground if that matters....