I've done 30000 km with a 190/50 size and now 15000 with 190/55, mostly 2 up. It takes much less effort to hold the bike on a steady radius when riding in the mountains or on a winding road through the forest. At speed, with the 50 size I had to use a good amount of force to keep the radius, with the 55 the bike falls effortlessy in the bends.
Stability at top speed is (I think) still the same. Tires now: Michelin PR4/GT

They were that way from purchase with stock tires? Pretty amazing.  I have never had a vehicle that matched GPS speed.  Had one that was close, though, like 1MPH or so over.

same here, my 2011 ford super duty shows 75 and the gps 74, which is pretty close. no doubt my bike is off.

So I jump in here because Saturday I am going to drop the bike off for tires and the only decision I have made is I don't want the stock ones back on.

Suggestions?

Michelin Pilot road 4s in the 55 series.
They made a tremendous difference in mine and seem to be lasting well.

There is also a 180/55 available.  I went with that initially vs the 190/50 because at the time they hadn't brought out the GT-spec tire in the larger size.  The 180/55 turns in MUCH faster than the stock 190/50, while the 190/55 is only somewhat faster.  The new PR4s in 190/55 are crazy good, especially in the wet.  None of the changes are worth swapping a non-dead tire off for, but are definitely worth the $10-$20 difference in tires when you've worn the originals out.

same here, my 2011 ford super duty shows 75 and the gps 74, which is pretty close. no doubt my bike is off.

So I jump in here because Saturday I am going to drop the bike off for tires and the only decision I have made is I don't want the stock ones back on.

Suggestions?

PR-4's, when second best will not do.

PR-4's, when second best will not do.

But that is the second best.... you really want PR-4 GT's

It's neither the size of the boat nor the motion of the ocean. Its wether or not the Captain can keep it in port long enough to get the all the passengers off

It's neither the size of the boat nor the motion of the ocean. Its whether or not the Captain can keep it in port long enough to get the all the passengers off

That, I get.  Never heard this one before. 

61,  Happier  with the 55 or the 50?

Like the others say, the 55 is just more responsive in leans.

mat

I read here, someone said that he aired up to 46 LB's front and rear, and got great response with a 50 series.  I aired up F/R to 45+ and took a back road ride today.  The bike dropped into turns and was easy to keep it there, with that air pressure.  It's higher than the 42 recommended, but the Z8's really performed. 

Kinda like a KLR650.  Kawi recommends 22 LB's F/R, a setting that totally sucks, both on and off road.  Use 30 in both, and highway travel is smooth and tires last.  Off road, around 12/16 LB's works.  WTF does the factory know, anyhow???

I felt no difference other than the difference felt when putting any new tire on a bike.  I do set up my suspension for my riding style and load on the bike.
I will probably go back to a 50 on the next tire change.

I like the 190/55, but the next one on will be a 200/50. Will see how that goes compared to the other two.