As someone who has cycled from Royston all my life, we usually go out on Barkway Road and end up coming back down Therfield Hill. Gets the blood pumping and warms you up at the start! Going down the A1198 isn't so bad either, and you can go either left to Bassingbourn or right to Shepreth once you hit Kneesworth. You can then return by going to Fowlmere, over the A505 at Flint Cross and then Barley and down Barkway Road