A rough track with a lot more power was my situation this year. Usually there is minimal wheel slip and the gearing was set without considering it. The wheel did slip, the engine hit the rev limiter, and this put a limit on the top speed.
The flip side of the coin is the tractive force is reduced with tall gearing. if the reduction ratio is too small to start with and you do not get the anticipated wheel spin, you could'a gone faster.
Being prepared for a gear swap, like you are doing, is a good idea. It is hard to get the ratio right until a run is made and there is a chance to get some data and do some figuring.