equipment recommendation - Which laptop has the best display for photographic processing?

I'm planing to get myself a new laptop for processing my shots in Lightroom. I shoot in RAW and then process all my images in LR.

I'm looking for a laptop, 15.6 inch with the best LCD. So far I've been using old Dell XPS and I was very pleased until recent failure of LCD itself. I know that the best results I can get by purchasing external display such as NEC Pxx series, but for me this is not an option as I need portability.

There is one more constraint, it must be Windows laptop, no chance for switching to Mac.