2nd screen/monitor

I have small studio with limited space, I currently have
1 x Apple 23" display
1 x small 10" CRT monitor , connected via a Kona LHe card, which I don't always use

I have been thinking about buying a second Apple 23" display to give me more canvas area for editing
but then I read bob Zelin's article on calibration and thought maybe I should get Dell 2407

"he absolute cheapest "very good" quality HD-only monitor is the Dell 2407WFP, that sells for around $700. You use the analog HD YPbPr signal from your video card to feed the RCA inputs of this monitor. It works just fine"

my questions are should I connect directly [keeping the kona connected to CRT monitor ]

or via Kona card [this way I would really be able to have double canvas area

also can't find Dell 2407WFP for sale in UK
only Dell 2408WFP or Dell 2409WFP what the difference and is there some other monitors I should look at?

thanks for your help
Mikef