Why OLED? Is this indoors? Outdoors? Under what lighting conditions?
Variable light conditions from full sun to night time, plus OLED more for viewing angle.
I'd considered 7 segment display, the reality is though that it's fixed, dependant on how many segments it has. The other reality is colour scheme. It doesn't really lend itself to high contrast black on white for day time use, then night friendly colours - which obviously can be achieved with an LCD / OLED, although LCD has the back light on continuously.
And Liudr, yep, that is also the plan, which ever screen I use, I'll be doing that anyways... for whatever key point of information is in the spotlight at that time (I'm thinking ahead - forgive me)