There shouldn't be a noticable perf difference between x and y. The new vision code lets bots see a little further in y then they did in previous versions (I.e. they see the edge of fat bots, not their centers and so it's possible a few bots that were out of range in x and now in range in y and that is impacting perf a little) but I would not expect this to be noticible much less 2-3X slower. I do not see any perf difference myself though it is possible I screwed something up that is specifc to your environment.
Your using the same exact sim starting from the same cycle in both versions to test, yes? Could you post your sim so that I may investigate? Thanks.
Oh, and welcome aboard.