In the case you have to get it all done anyway, and you have the cash, you may as well upgrade to 4 pots.
 
Just bear in mind you'll probably need to fit a pedal box, or change the master cylinder, at least if you want the most out of the upgrade.
 
A set of princess calipers and rotors just went on eBay UK for around the 130 pound mark so keep an eye out.
 
Cheers,
 
Matt