Input lag will be higher on good tvs vs good monitors. At least look at plasmas for better response times if you go for tvs.
I think each option has it's good and bad points...
Is their a super fast panel beyond the 27"-30"? If their is it will likely be expensive.
For the gamer used to a superfast response monitor lag may be more of an issue or factor. In general we do not see forums littered with people complaining about over excessive lag on their new HDTV purchases.
Most of the TVs nowadays also have a game mode which helps but if lag is a problem for the user then really a fast monitor may be their best solution. You have to factor what is more important to your personal needs.
Plasma can give better blacks (not on all models and it is noticed more in a dark room). Yes they have faster response too but you still can have screen burn issues with plasma technology. I have a 50" Pioneer plasma at home but it is a behemoth compared to these new super slim LEDs.
A decent HDTV will easily outperform TN based fast panel monitors regards black level and quality of image. Likely less light bleed too often found on monitors. The contrast and clarity with good modern LED models is rather amazing as is the value now too. 40"-42" will be the sweet spot. Expect a couple hundred more for the 47-50" sizes.
I remember my first triple screen for Forza 1
3x Xbox £300 each
3x VGA adapters £50 each
3x Samsung 193P 19" Monitors £500 each
So the price and what you get these days is a heck of a lot more for your money. Mind you I think few people will be buying 3x Xbox One for triple screens at the start with FM5.