Which NEC monitor?
And would one be noticeably better than the other for sRGB - or is this just splitting hairs?
I'm not sure what the preset sRGB mode is like on the P221. There are a lot of reports here that with the PA241w the preset sRGB mode is very very good.
I would think that you would likely not notice any difference viewing a sRGB image on either in their native custom mode, provided you have your color management issues under control with the P221.
You've read the reviews?