2 x 460s is overkill for that resolution and I think any processor will bottleneck it a bit. You should get around 3.8-4GHz from either the 955 or 965 on air (with a top end air cooler) or 4.2-4.5GHz with good water cooling (I am only going by what other people in the forum have said). I would suggest you get 1 x 460 now and get the second when they are cheaper as I don't think only 1 will limit games much at that resolution and you are certainly not going to fully utilise 2 on anything at that resolution. Alternatively if you are going to upgrade completely next year you could look at a cheaper option like 2 x 5750s. I can play all recent games I have tried on maximum settings at 1920 x 1080 with my old single 4890 with good frame rates.
You can't ensure there is no bottleneck. There will always be a bottleneck. When you fix one bottleneck something else then becomes the limiting factor in performance.
If you're getting SLI GTX 460s to remove a GPU bottleneck you might next have a bottleneck in HDD I/O. Add a SSD? Then you might have a RAM bottleneck.
What part of your PC is the bottleneck will depend on the application or game you'll be running. It won't always be the same part.
If you're gaming and your system reaches a performance bottleneck at 85 fps in your game does it really matter to you?
On the other hand if that bottleneck occurs at 15 fps can you afford to spend the extra money needed to get around that?
It's usually easier to adjust the in game graphics settings from Ultra+EyeCandy to something that gives you good performance and pleasing graphics.
Don't get the factory overclocked GTX 460s. You can do yourself what the factory is charging extra to do for you.
You might be able to get a X4 965, aftermarket CPU cooler and 2 stock 460s which you can then overclock yourself for the same price you'd pay for a X4 955, no aftermarker cooler and 2 factor OC'd 460s.