There are things that can be done to help minimise the differences. If the subject aeroplane (or helicopter) is much slower, then putting it on the inside of a turn helps. If it is much faster, then a wide descending turn gets the speeds closer together - there's nothing worse than a picture of a jet with gear and flaps down and at a high angle-of-attack, or a speck in a blue sky that's actually a microlight lagging a mile or so behind.
Yesterday's subject, a BN Islander, was ideal - the Islander will fly at stupidly slow speeds or will fly at up to 130kt (which is also stupidly slow when you consider that it takes 600hp and the associated fuel burn to do that). It was also being flown by someone who teaches formation flying, which made things even easier.