I've just swapped to wide gamut and I wouldn't go back. The extra colour depth is noticeable and I really appreciate it for skin tone highlights.
However, wide gamut comes with several caveats. You really need a solid understanding of colour management or it is likely to bite you in the ass.
When you say the Dell "should be calibrated"... I would like to correct this. Dell will send your monitor with a factory calibration report, usually stating that DeltaE (the measure of how well colour is calibrated; lower is better) is < 5 or something. This is 100% lies. My U2410 came with a calibration report stating average DeltaE was 4 (which is 'okay' but not really acceptable for colour critical work), but when I measured DeltaE with my i1 display pro, it was actually around 10. In fact, the monitor had a distinct cool green hue to whites.
Now that I've calibrated it myself using the i1, average DeltaE is 0.7 with max of 1.3. Pretty good by any standards.
Regarding the PB278Q, here is the tftcentral review: http://www.tftcentral.co.uk/reviews/asus_pb278q.htm
His model came with a maximum DeltaE of 10 in the blue hue measured... which is pretty bad to be honest. Average of 3.4 is not awful but not great either.
RE: The Dell 2713HM, it had a DeltaE average of 2.7 with a max of 5.7. So slightly better.
In a nutshell:
1) Wide gamut is useful for printing because some printers are capable of displaying a wider gamut than sRGB. It is not particularly useful for web display, and can even be detrimental if you forget to convert your photos to sRGB for web use or when sending to other "non photo" people.
2) A good monitor is only as good as its calibration and all 'out of the box' calibration is pretty rubbish. As a photographer you shouldn't be saying "I have x budget for my monitor", you should be thinking "I have x budget for my monitor and calibration equipment"