I have a 40w5500 and am very happy with it, this is my second set as the first suffered with clouding in the top corners but the replacement is great and no clouding. I have to admit that with all sources i am thoroughly satisfied as the difference between this and my old Sony P3020 32" is night and day...i would stress as you said in your post that you need to be able to exchange the TV if you are not happy as some sets certainly suffer with the clouding so get a decent retailer and i think the choice is easy, it has to be the 40w5500.
Thats a load of rubbish about flat colours by the way! The W5500 has a Live Colour setting which sorts out any 'flat' colours, it works so well that i have never needed it up any higher than low if atall, i only use it for standard def anyway as you really don't need any processing when using hi def!
Sony KDL40W5500, Sony STR-DG820 receiver, Q Acoustics 1010i 7.1, Soudstyle Z2i stands, Sony PS3 SLIM, X-Box 360, QED Silver Anniversary XT, QED HDMI-P, Tacima 6way block, Virgin V-Box.