@OP
First of all, With your Monitor there is no point in using SLI or CF.. Becoz your monitor resolution is a wall for SLI or CF ,mostly depends equally on CPU and Vid card... (Sometimes depends on Game too)..
SLI or CF is used for massive resolution such as 1920X1080 or more.... So stick with single card for now..
SLI or CF,, Before you Buy, make sure your fav game supports SLI or CF... I am using SLI right now,, almost all my Fav games endup with no support for SLI or CF...
Not all games run perfect with SLi or CF becoz of game design.. Example Starcraft II wings of Liberty plays with only single card well and with SLI or CF ,, Frames suck..... There are many out there and both Nvidia and AMD are struggling to get good drivers for new games.. This is the Dark truth and 100% fact.. 3Dmark 2011 still doesn't support SLI ,only hacked drivers are able to run but system crashes...
YOU DON"T NEED SLI OR CF for your MONITOR. NOTE this point or else you will regret later for wasting money....
For you Nvidia 560 or AMD 6950 is too much right now.. Get it , you won't regret at all. All games will run max settings with your monitor.....
EDIT: Even for 22'inch monitor nvidia 560 or AMD 6950 will do better.... I seriously suggest you to stay away from CF or SLi.. No offence.. you will face lot of tensions for solutions to run games in SLI or CF...
SLI or CF ---> Heat, More current Bill, More Noise, SLI or CF issues wait for updates..
(if runs in SLI or CF,, Games are piece of cake in max settings)
Single ---> Less heat, Normal Current Bill,, Low Noise, No issues runs all games out of box. All is Well
(not all games run in max settings)
My Current Bill have suddenly increased 600rs for normal weekend gaming.... Imagine 10/7... then