Normaly i use osd to see the fps on a game only when i am still on the procces tweaking my settings normally i aim 60 fps so it helps me decide if i should rise details or lower and see what i am willing to forfeit. After i am done with that osd goes off and never gets on again!

I use smallest vector font for OSD in RTSS. Most important thing for me there is Clock. And I do use less bright settings for OSD colors. So it is not distracting. +top right corner is not used by games much. For me, frame rate is good anywhere between 1/2 of monitor's refresh rate and full. 72~144fps. Fps lower than 72 feels like slideshow.