I do a lot of EDI/EWR/IAH for work so usually take the CO37 EDI-EWR & CO811 EWR-IAH, which gives about 3 hours connection time. Having said that it's personal choice rather than necessity. I've never been more than 20 minutes from landing to being back airside & walking past where the next flight to Houston CO23 is due to leave at 13:30, rather than the 811 which leaves at 15:00.
I just like the chance to wander about, stretch my legs & get someting decent to eat in a fairly relaxed environment just watching the New York skyline.
90 minutes is plenty, but don't worry there's plenty of back-up, even if you do get delayed.