I have had an Evolution Chips remap on my facelift 320cdi CLS, best £300 I've spent lately.
They say an extra 37 / 40 bhp and 10 / 12 % better ecomony.
Its definitely quicker and has much better torque, its showing 40+ mpg on long runs too, never seem better than 37 before.
Had mine done at Lenwade near Norwich but they have agents all over country, they read the current map and then get a better one from Evolution within an hour, job all done in 2 hours or so.