I would say no, but it also depends on what the price difference is.
A Radeon HD 7850 would mean you really don't need to upgrade the graphics card for a long time playing @ 1366x768 resolution. It also opens the possibility of buying a higher resolution monitor, but w/o the need to buy a more powerful graphic card... at least for a little while depending on your performance expectations.
On that Resolution you really don't need a 7850. Get the 7850 only if you will be upgrading your monitor soon otherwise there's no point as a 7770 will max out all current and upcoming games at that resolution easily.