Its right gtx (2)460 will be a great deal for you so you should go for it....also if an single gtx 460 is overclocked it can reach nearby to the gtx 480 ..by this you can imagine the power of gtx 460....so think what 2 of them will do...
There is no way that the single (overclocked) GTX 460 will reach GTX 480 performance, it will be more along the lines of a 5850 from ATI. Please read below for proof...http://www.guru3d.com/article/geforce-gtx-460-sli-review/1
@ OP, Consider how long you will end up keeping the new video card or cards, if you plan to keep it/them for at least 1 and 1/2 years then leave the 285's out of the question. Now, since the 285 is roughly the same in performance to the 460 and the 460 is cheaper, i would definitely consider the 2 x 460 option. It will perform better than the GTX 480 in almost every title while consuming less power, less heat and overclocks very well, all while being cheaper than the GTX 480.
As for brands, that is all preference but i would suggest, that since the 460's are smaller cards, that you go with the MSI's as the cooling is great on those things.