It's difficult to generalise, and I don't know much about Sphinxes, but Tonks are personality cats, and I suspect the same applies to Sphinx. A boy cat is frequently more laid back than a girl and personally I usually prefer to have a mix, but when I have had same-sex households they have been boys, not girls, because they get on better. I am afraid it is a case of suck it and see really ... If the boy is still fairly young that will also help