I know Calic who did 5.5cm (sorry I forgot exactly how much) was also in your shoes. He had the longest tibae out of all the patients at my farewell party. You should breeze through his diary.
Base on the pic, I agree with Chris. I think you can easily pull off 180cm. I was going to say your 185cm looks natural, but when you said that your shirt reached the bottom of your groin, then I would think that your legs would be too long in relative to your upper proportion. Honestly, if I had a wingspan of 185cm, then I wouldn't mind going for 185cm myself. However, I'm already reaching the limit as you can tell... so 3-4cm more would already make me out of proportion.
Changing from 5'6 to 5'9 and I go outside every day, no one commented on my proportion. Everyone just commented on other things. So I think that in general, the people on this forum is a bit proportion obessessed. Even a girl who I valued her opinion (because she is blunt) said that the only thing she notice about me is that I'm well dressed. Period. Maybe that's because I'm still under average height... so I can't same say the experience would be the same for someone who goes from 5'8.5 to 6'0.
If the bottom of your groin is 2 inches lower (and not at your shirt), then your 185cm photo looks like the model below.