Right now you are on a 63.0 inch gear. That is pretty light for the street. You have a choice. You can pick up a 19t cog, and use it with the 53t ring, which would give you 75.3 inches. An almost perfect street ratio imo. With the 42 ring you could go with a 15t cog and that would give you 75.6...also a really nice gear. Since you have both rings already I would go with the 53x19 set-up. More teeth equals longer lasting. When that finally wears out you can go with the other set-up and it will be roughly the same gear. Good luck and happy skidding.