gyzzzmo was very happy in his remark: there is no fixed speed to any piece. even when the composer himself puts a metronome mark, it must not be regarded as a law (the reasons to that are subject to another discussion).
anyway, in the academic approach we do have boundaries, and between them you are safe and fine. an allegro to chopin means a fast moving flow, but not an absurdly fast moving flow. he did use his presti quite precisely.
just for the sake of the argument, i mean the academic approach because outside this, you simply do what you want to the piece. wanna play this piece at 40 MM, go and play. btw, a lot of people will love it, and some will actually think that your is THE version. if you have enough lobby, you may even reinvent chopin.
it happens all the time!