well... really depends on what you want to do.. I use the delta's for high clock runs and benchmarking they are very loud @ 100% RPM and not for everyday use at that speed... 24/7 I run at 3.825ghz and the fans run along at around 1400 RPM as the rig folds 24/7 at that speed they are not to bad and still keep things cool (100% load @ around 55c across the cores)..
Also you need to consider what your motherboard and CPU will do.. no point buying deltas (costs around £17 / fan to ship from the US) if you setup wont do the clock in the first place... I wouldnt recommend buying the model that is stocked by UK e-tailors its two powerful, two loud and can't be run off a 3pin mb connector or fan controller and therefore you have no control over its speed... If you look in my christmas eve overclocking log there is the model number for the type that I use which can be run off my P5K-E 3pin fan headers (althought would check your board can support the amps/watts)..
Alternativly if you want some more ummphh but dont want delta's I have found the Sharkoon Silent Eagle 2000 to be very good fans, which are quiet and put out some decent airflow... a laped TRUE with 1 or 2 Silent Eagle 2000 strapped to it would give you a nice boost over your Tuniq
