The brakes on these Fiestas are just crap in general, you've replaced them with harder items so yes I would expect a change along these lines.
Be careful with the Groved and drilled stuff though, they crack very easily, avoid going through puddles as it'll cool them too quick. EBC pads for £20 though? Link?
Not true, drilled discs do not crack easily, I have heard that if used for racing this can happen. Fitted a set of drilled discs to a Merc CLS, these have now been on for more than 5 years, no cracking, these dicsc were also purchased from MTEC. If you buy EBC red stuff than you can double the price of the pads. Check the prices for yourself