A lot of us like this graphical gearing calculator:
I set it up to compare 44t and 36t chainrings on a 9-speed 11-34 cassette at an arbitrary cadence of 70 rpm.
The number of rear cogs is irrelevant here, as you're only interested in the ground speeds given by the smallest and largest (11t and 34t) cogs at your cadence(s) of interest. These speeds appear above the inverted triangles.
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Put in the lowest and then the highest cadence you're comfortable with, take a screen shot of each case, and compare the screenshots.
NB: This says nothing about how fast you can go with a given motor and rider power input. For starters, you don't have the data needed to estimate that.
It only says how fast you'll be going in a given gear at a given cadence with a given wheel diameter when actively pedaling. Whether you could actually reach that cadence in that gear on your ebike is a separate issue.