My three cents: How big can you sell? Bigger should equal more money to you and be more impressive as a presentation.
Years ago a portrait teacher said he often used to put up a really big print of a customer at an easel in the front room of his studio when the customer was coming in for an appointment to see the results of a session. The print, he would tell the customer, just looked so good he was using it to show other people how good a portrait he could do. It wasn't something the customer had ordered - just a really great shot. He said the customers would often buy the print. It was the equivalent of "spec work", i.e. speculative, but often worked.
Best,
C