Performance of EMU7800 emulator the Atari 7800 should be more then adequate on most hardware. It is also capable of running the vast majority of the Atari 7800 games that are available.
In fact the most recent versions of the EMU7800 emulator appear to only be working on porting the emulator to more systems with no real changes being made to the core emulation. This can be a sign that the emulation core is as solid as it really needs to be.
In addition to primarily being an Atari 7800 Emulator, EMU7800 does also include support for the Atari 2600.