One thing to bear in mind is that the Clubmans will only allow ESCs from a certain list. The BRCA site is unavailable for me right now which isn't helping, but its worth checking that your ESC (and certainly the one you are thinking of buying) is actually on the list.
The BRCA list has until now been mostly based on the ROAR list from America -
http://www.roarracing.com/?page_id=737 - and the LRP version of your current speedo is approved, as well as the Losi 9500. That doesn't guarantee BRCA approval though so you should check with the organisers.
As far as the ESC goes, if it has been working well for you until now, I don't think there will be any advantage from going to a different ESC - that is the brilliance of blinky, the ESC (assuming it can cope with the motor) doesn't come into it. If you find that the ESC doesn't have a good throttle feel or good braking (for example) you might like to try something else, but it won't make your car any faster.
I'll be doing some 17.5 blinky racing this season with a Hobbywing/Much-More speedo.