I actually can't stand using very large monitors for PC work. 27" is OK as a TV, but when you are sitting only a few feet from it, it's too big, your head is moving too much to see from edge to edge. At work, we have a 32" Planar 4k resolution display, cost about $10,000. No-one liked to use it. They prefer two different monitors side by side to that thing.
Unless you already though this over, try a 22 or 24" monitor, you may be happier with that, unless you sit far back and want to use it as a TV display also.
Personally I use a 27" ASUS and it's a great monitor. It's certainly a big step up from my old 19" CRT. I suppose it might be easier to focus on a 24" display if you are using it for work, but that's what I do and I have no real issues.
IMO the "ASUS VG278H" is the best 3D 120Hz Monitor available at the moment, especially with the LightBoost technology if you are using it for 3D (the older ones look too dark).
Unless something better comes along soon this is the display I will be buying when it's released next year in Australia.
It's up to you but after experiencing a 27" LCD for movies and games I wouldn't want to go back to a smaller one (unless perhaps it's three of em in surround)
Anyway good luck in finding the best solution for your needs.