Equipment Recommendations?? Brakes and Large Frames

Two things I'm interested in at the moment:

1. I need some decent brakes -- no... really good brakes, actually -- to replace the stock brakes on my 2005 Langster. 12 miles + round trip through central London every day means Lots of use, despite riding fixed.
   
   

I'm 100kg +, as well, so need something serious -- any recommendations?

1. The Langster needs replacement -- it's too small at 62cm and I'm thinking I'll have to have something built -- any ideas for good builders in London/SE England? Elsewhere?
   
   

Any ideas on either are much appreciated... thanks.