I would imagine you could use either just fine. On my BST 5.75 I’ve only used the 180/55 and 180/60 Supercorsa SP and SC. I find both a perfect fit on the 5.75 rim. On the 5.5” rim I usually have about 4-5mm of chicken strip I find impossible to reach. With the 5.75 I can use all the tread area.
I can say a 190/55 has the same theoretical circumference as a 180/60...but will sit roughly 1/2in wider overall...it's a slower rounder tip in...as a result...if I was dragging a body to feed to a tiger I would probably opt for the 190...lol
I have 2 sets of wheels for my track only 748r, Marchesini stock wheels that came on it, 5.5” rim, ran 180, got a set of mag Marchesini from Steve at the old ECS in NY, 6” rear, run a 190, the tires both look correct rim to tire. Tip in still felt faster with the 6” because the wheels are so much lighter, I know same/same wheels/tires the 180 would be quicker turn in. The CF wheels I like and am looking at stop at 5.75”, was wondering if the 180 would be more stretched or the 190 more bunched, which bridged the .25” gap better.
I've had the 190 and 180 on my 916, the 180, as most have said, does turn in a little easier, but not enough to make a difference for a weekend rider. I also had the 190 on my Multistrada and always on my 999R. From the balanced look standpoint, the 190 fills out the rear better and that is what I like about it. The 180 is just too small to my liking, but most people wouldn't even notice.
Toss a coin. She’ll be right. Something to not lose sleep over. Over the years as a general rule I’ve found flatter style profiles (Michelin) felt better on wider rims and rounder profiles (Pirelli) fell nicer on narrower rims.