the venice is the new core replacing the winchester, the main advantage of which is that it has an improved memory controller. this means that if you decide to add several DIMMs, that you wont have to run them at a lower speed as is the penalty of the winchester. this wont affect you if you only every use 2 memory slots, but if you want to use all 4, it will. the winchester is still a good chip, and worth the price discount at the moment, if you dont want to use more than 2 DIMMs.
the samsung is also good at around £60ish i think, but although is considered to be the quietest, isnt supposed to be the fastest. that said, i doubt anyone could tell the difference. it is difficult to compare hdds though, especially as many reviews dont take into account the difference in performance between different capacity drives of the same model family.
well, the abit is based on the same chipset as the Asus A8V, but it is both cheaper and passively cooled, which is nice. the A8V is not SLI as i know it, but the A8N is available as SLI for £95.
EDIT - the A8V-E deluxe comes with a wi-fi antenna, which is probably why it costs £20 more. so if you dont need built-in wi-fi, i dont think it's worth it.
there are cheaper case too, like the jeantec phong that can be had for £35 including fans. you'd have to go for something you like the look of though. the centurion i mentioned should be the 530 model