Langster / Langster Pro / Langster Steel

^^ yes the general consensus is they are the price point - but obviously the Ultegra ones will be better and the DA better than those... and I'm sure there are some boutique ones which are even better.

I'd start with pads and checking your cables/setup, bc the stock shimano pads are a bit shit anyway so you'd be stupid not to get new ones if you're upgrading. One of the good things about the fibrax ones* is they're cheap and you can get replacement pads for the holders. The only bad thing is they wear out quick... but then you've got to weigh up your riding style (ie you're riding out of town, not stopping every 5mins2mins for lights).

TBH it might be worth going to your lbs and trying to blag a test ride on a road bike with topend kit - so you have an idea of the limits of callipers.

I've never used really shit hot road brakes and its been ages since I've been on an MTB, but it seemed to me that when it comes to braking you're taking a whole different league...but then you'd wouldn't complain about a mtb having too much rolling resistance on the roads would you?

I guess my point is unless you get brazeons for disc brakes, you're not going to have disc brakes, so just learn to accept the limits.
*Chainreaction sell them

My relatively unexperienced view of road brakes was that yes it's worth spending so much, up to (£30ish a caliper) but after that point, the advantages are slight and mainly down to pad/rim combination and you might be better spending your cash on some fancy pads and cables (ceramic openpro's are twice the regular price). Shit tektro calipers and aztec pads are enough for me to lift the back wheel at the lights, fully seated, day in day out.

Check the pads still don't have the shiny box fresh coating on them and how they are contacting the rim before doing anything else. The setup on langsters is v-similar to most otp's, the brakes might not be stellar but they work.