I've tried wimax before, it's a joke. IF I could even get a signal, which was rare indeed, I never saw anything above 1mbps. My UPload speeds were even more of a joke as at times it was hitting like 5kbps. Or it would just say network error and the test wouldn't finish. And that's in the city.
And I must admit I am not familiar with metro pcs plans, as they are not nationwide and not in my area.