A 35.9 300m should equate to something like a 49 mid.
As I've said before on these forums I'd be cautious about making 55-100m extrapolations as they leave too much to chance to be accurate.
Check out the mercier tables for time equivalents (not necessarily the same as extrapolations):
https://myweb.lmu.edu/jmureika/track/Mercier/index.html
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