Which is the Best Tuning Upgrade for 2.5 DT?

Has anyone fitted an ECU upgrade (chip etc) and Larger Intercooler and can you advise best upgrade ???

I had my 2.5dt chipped a few months ago £499.00 the garage told me a new intercooler would be a waste of money as the differance would not be noticable, He said a k&n filter would make a slight differance for a fraction of the cost. After having my one chipped i have noticed no drop in mpg
regards andy

a mate of mine has had his 2.5 chipped with excellent results!

edit.
or drop in a V8