I would just change the pads, The Clarks one in the link above are very good. My Secteur came with cheap Tektro (I think) brake calipers, the brake pads that came with them were absolutely shockingly bad. I changed the pads to the Clarks CPS240 ones and the increase in braking was brilliant. To see if I could improve them even more I bought a Shimano 105 front caliper and put the same Clarks pads in them. I could not tell a shred of difference and it was money wasted for nothing more than a nice 105 decal.
I read a lot of bike reviews and it always seems to mention the bike is let down by the cheapo no name brakes and it should have Shimano 105 like the rest of the bike etc, etc. From my limited experience I would guess that it is the 105 brake pads that comes with the 105 caliper that probably makes the most difference to the braking, not the caliper. I guess maybe the calipers on my Secteur were good anyway, certainly looked little different to the Shimano ones. Just from my own experience with the one bike by the way...
