I assume that by 540 can motors you mean the non-rebuildable 'silver can' motors?I don't typically run those but I can vouch for performance improvement on 27t and 19t motors by upgrading from low-end speedos to G-11's or LRP QC2's for off-road. The way they handle current and offer more high-RPM power simply can't be ignored.
IMO if you have well-maintained motor and packs, you will definitely see a performance increase by trading up to a higher-end speed control that was custom-made for the specific type of racing you're doing. I'd be very surprised if you didn't notice a difference with the LRP TC over a $50 cheapie.