Crucial has just released a new firmware for the m4 drives which increases performance quite significantly.
Download here:
http://www.crucial.com/support/firmware.aspx
My benchmarks before/after (128GB model advertised speeds Read 415MB/s, Write 175MB/s)
After
Overclockers currently has a sale on crucial drives
http://www.overclockers.co.uk/search...m_medium=email
£148.94 from scan for 128GB model
http://www.scan.co.uk/products/cruci...-write-175mb-s