Once you get the computer see what your speed is at the 90 rpm on a flat. That will tell you what your speed is at that rpm with your bikes gearing. Once you know what your speed is with your gearing. then you can consider if changing the chainring to a larger gear or the small gear on your rear cogs. I was surprised how much a 50 compared to a 48 in the large chainring made between my two bikes with the same 11 tooth rear cog. Just another idea but listen to the advice given in the previous posts first as I do not have the experience that so many others here have.
Frank.