I have not driven on a flat run-flat despite having had several cars with them (my current BMW and several Corvettes). But I know people who have and they say you cannot even tell they are flat. I will tell you this though, if you think your car rides well with them you are wrong. If you switched to non-runflats you would notice the difference within a couple of miles. I know that because I've switched several times on my Corvettes, and I can tell that my BMW has runflats. You must have awfully good roads where you live if you can't tell.
2012 BMW 550 M-Sport
2014 Lexus GS350---Wife's car
2013 BMW 1600 GT---2011 Kawasaki Ninja 1000---2012 Ducati Panigale