I'm doing it... Tour of Flanders (Ronde van Vlaanderen) ride on 04 April. I don't have the fitness to ride the full 256km. So, I'll do the 140km ride.
I think that 90 miles on steep, cobbled roads (in the cold/rain) should be adequate to confirm that I don't have what it takes to race as a Belgian Pro:-)
I think it will be a ton of fun.