hookyThat page is confusing. Only the version without speakers is the XL2411Z, and it's £225. The £132 one is the RL2455HM, and it's just 75Hz. The £290 one is the XL2420Z, and the one with game mode is the XL2430T.
So, go for the one that says "HDMI, no speakers." That's the only one there that's the XL2411Z. If you can find the XL2420Z for cheaper though, do that. Both are 144Hz. If you're willing to go with 120Hz, then you could get the XL2430T, but I'd just go with 144Hz at this point.
DP means DisplayPort. It's not necessary as long as you have dual-link DVI (which all of the XL monitors do). It's basically an HDMI-like standard used mostly for monitors. It supports much higher refresh rates than most implementations of HDMI. But it's not necessary if the monitor has dual-link DVI (DVI-DL).
Very, very helpful, answered all my questions and more. Thank you. :)