No, the GTX260 is faster.
Do not worry about the HD5770s DX11 capabilities, from the tests I have seen and done the '5770 is not fast enough to use the new tech without suffering a huge performance hit.
I would just hang onto the GTX260 instead of a 5770. The new card won't be much of an upgrade and in some games will be a significant downgrade. However a 5850 or better then sure they wold be an upgrade.