slow bike...is it the chain?
One note is that the gearing is different, assuming they're still stock.

The Specialized Langster London has a 42t chainring and 16t cog, the 2013 Langster has a 48t chanring and 17t cog.  With 700x25 tires that means they are 69.6 and 74.6 gear inches respectively.

What that means is that spinning at 100rpm, you're going ~22mph on the Langster and only ~20mph on the London.  So it will feel slower when you're trying to go flat out.