If you are the kind of gamer that really gets into it getting very close to the monitor say 12 inches from it,go with the 24",if you sit back from it a little bit i would go for 27".But remember bigger is not always better gaming,If your eyes have to scan from right to left to notice movement where your not focusing on,sometimes smaller is better.
Believe it or not 3 inches adds alot of screen space compared to 24",kinda like going from a 42inch tv to a 50-55"tv,so pick your size wisely,its personal preference.But i do know for sure you will love whatever you do end up spending your money on since anything is a upgrade:)
Technically its more like going from a 47" to a 55"tv wise ,doesnt sound like much but i did the same switch basically 46" to 55" and i have to say holy cow the tv looked much smaller in the store with all the other ones around:)
But hurry up and pull the trigger on something:)I used to have a 24inch back in 2004-2005 when they first came out from dell and i loved it,was $1000 and it was worth it back in the day since i was a nascar racing 2003 sim racer,the extra width going from 1600-1200 to 1920-1200,helped me see people racing right next to me door to door without having to look to the right or left.
Sigh,I miss my race seat act labs shifter wheel and pedals:(
Second edit,looking at your choices and it looks like you like big like me,i would get the LED asus 27" I personally feel leds give you a richer more uniform picture,but that adds a few bucks,but i feel its worth it,LEDs are much brighter and last longer then cathode ray tubes.
ASUS VE278Q Black 27" 1920x1080 2ms Full HD HDMI LED Backlight LCD Monitor w/Speakers 300 cd/m2 ASCR 10,000,000:1 http://www.newegg.com/Product/Product.a ... 6824236103
2600k HT on@4705mhz 8gb Cas9 1600 mem 2x EVGA GTX770 4gb Classified cards in SLI @1320 mhz core and 2003 mhz mem,mounted in CM HAF922 with a TX-850 PSU 2xHTPC's 2xi3 2120 3.3ghz dual core,1xasus LP HD6570 1xHIS hd7750@1150core1325mem,55"PanyVT30