This is from Sodas Aircraft page on behalf of the fine Hurricane Mk1....
"Top speed at sea-level is only 253mph (261mph with WEP), increasing to ~320mph @ 16K."
And i can vouch for lots of GVs timidly running instead of staying to fight!! Dweebs

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Edit: just did some testing in TA: Top speed at sea level 252 mph, 260 mph(with WEP).
A quick google showed no info on top speed at sea level. Maybe someone can dig up reliable sources?