I always prefer to cook mine slowly, I put some seasoning on first and wrap it in foil and then cook on low heat. Not everybody's choice of cooking but I have to say that all my visitors comment how nice my meat is. I use the juices that come out for my gravy.
Maybe you overcooked it. Silverside should be OK if you got it from a reputable butcher. It shouldn't take long in an oven at 200C, I cook mine for about an hour and I get a joint about 3lbs
I agree with vicmarion.
Cook it very slowly in tin foil on a low to medium heat. Use the juices for home made gravy.
I usually cook my joint for about three hours depending on the size of the joint.