Some work done at UCL regarding bitcoin and speed:

• HOW to crack bitcoin passwords at a very high speed: brainflayer cracker where we read that:
  “The bulk of Brainflayer was written by Ryan Castellucci. Nicolas Courtois and Guangyan Song contributed the code in ec_pubkey_fast.c which more than doubles the speed of public key computations compared with the stock secp256k1 library from Bitcoin. This code uses a much larger table for ec multiplication and optimized routines for ec addition and doubling”.
• HOW TO MINE bitcoin data at a very high speed: a tutorial on how to acquire and transform Bitcoin core data to an SQL database and mine this data at a very high speed (up to 50 Mb/second, the fastest solution known). See UCL bitcoin transaction data mining tutorial.
• HOW to design a faster crypto currency and could bitcoin be fast and efficient?: a vast question not yet solved in a satisfactory way but there are definitely some ideas. See Courtois-Emirdag-Nagy paper “Could Bitcoin Transactions Be 100x Faster” in proceedings of SECRYPT 2014  and here is a poster presented at the same conference. See also Section 7 inside this paper here, some other posts in speed category, and here is our video interview about these questions for the Financial Times. Related work: see bitcoin-NG proposal.