Your options would be something like
1) [1680 x 1050 20.1"] + [1680 x 1050 22"] + [1680 x 1050 20.1"] This would look ok the aspect ratio would be fine and you would have a slightly bigger central display. The Dell P2210 would be fine + 2 Dell 2007WPF.
2) [1680 x 1050 20.1"] + [1920 x 1200 24"] + [1680 x 1050 20.1"] The aspect ratios match so it would look ok but the centre monitor would be quite a bit bigger. Would possibly look bad. Your options for 24" 16:10 with Displayport are slim and expensive so would be better off using an active adapter.
3) Sell the Dell 2007WPF and go for 3 x 22" monitors. Dell P2210 + 2 cheap TN based DVI monitors. I would go for this option the cost wouldn't be much more than using the 20.1" because the price difference is small between 20.1 and 22". The satellite monitors wouldn't need to be the best something like
http://www.ebuyer.com/product/159417. This combination would provide the best experience.
With 1 and 2 you would have problems with Bezel compensation.