Roddick I am really unsure of. Hes lost to all the young guns this year, and his "DC till I die" attitude since USO has cost him some points he could have easily earned in Madrid and Paris. He will still serve big and stay in the top 10, no doubt. If Gasquet and Murray do what they're capable of and pull it together, as it seems both have done better this year, Roddick is outclassed and will be in the 6-10 range.
As for Davydenko, i think that is more wishful thinking on my part
The guy is way too boring and consistent for my tastes. SF/QF of all 30 tourneys he enters cant last forever. Also, the gambling allegations and watchful eyes of ATP might take a toll.
Fair thing on Roddick but what I said about the consistency is still true and Gasquet can win a tournament beating Roddick on the way and then lose 1st round three times in a row and if Roddick plugs away with SF's and QF's he will still be ahead. The season is 11 months not just a few spectacular performances and this is coming from a Gasquet fan.
Davydenko is boring on court but his tennis is fantastic, probably the most attacking baseliner in the world who doesn't have a big serve. Well, the thing with Davydenko haters is they all attribute his success to playing all these tourneys but the fact of it is he has tremendous results where it matters most although watching him choke over and over in slam SF's isn't great fun.
Nalbandian is one we will have to watch for. I still don't believe he will come back to the top 8 consistently but I think winning Madrid will have given him belief he may not have had for a long time. I don't think he would've beaten a top form Nadal in Madrid due to confidence but Nadal's weak performance and his great one gave him the confidence and once he had that he was a joy to watch at times.
My own opinion on Murray is that he is going to be like Roddick in that he gets the job done against weaker players and this is probably due to his good tennis brain and variety. He can use whatever he needs to use to get the job done and no it isn't always pretty but that's tennis for you. However, unlike Roddick, I think he has the technical ability to go head to head with the top players and come out on top every now and then. He isn't ever going to be as good as Federer on any surface but he can probably beat Djokovic a certain percentage of the time on all surfaces but clay and the same goes for Nadal.