I have been struggling as well, especially in the lagging bit. After asking and reading many questions as well as answers all I did was change the channel of WiFi to an unpopular one and it worked. Apparently when you install your router, it sets itself to a default number. Now usually everyone once they get a new router they install it without looking for any open channels or at least one that is not popular. Once I have done this it solved my problems, YES I simply tell you that it is possible but all it does require is a little bit of investigation on your side. All the tools are available for you and the research can be done by you.
Simply do the following (on a MAC of course):
1. Click on the "Spotlight Search'
2. Search for 'Wireless Diagnostics'
3. A new window will popup with an Introduction, which you can ignore since the application is what you need
4. Go to the menu and click on 'Window' and then click on 'Scan'
5. If the window pop's up and it's not populated with information, simply click on the 'Scan Now' button on the lower right corner
Here after completing the steps above you will find a window that includes a summary of your surrounding area's reachable WiFi routers (including of course the channels) that can benefit your research. Not that what I was hiding matters but thought it would be for the better.
Now lets look on the left side of the screen and you will find in the bottom two lines what is the best for you. In my case I need to look in the 2.4 GHz Band and says 6 or 4. You can follow their recommendations or you can go for your own by looking on the right side of the window and look at other routers have their channels on. As shown below none of the other routers are on channel 4, 5, 6, 7, 9, 10 running on Band 2.4 GHz. I can use any of the open ones and settle with for now. Next step would be updating your channel in your router. It should be in your wireless settings and I leave that for you since there are different routers out there with different settings. But to make your life easier is simply go to the Wireless settings on your router and you should find an option with the Channel next to a pull down menu where you get to select your chosen channel.
Once I completed this, I found this working better than OK and tested running a movie on VLC (a video media player) and seemed way better than before. The only problem I found is that when I run streaming channel for example watching a soccer game it was not fully smooth but it was OK. But watching a movie on a media player was good or even watching a soccer game that running from a file and not from a streaming site worked smoothly. I guess the streaming problem still presides on any PC/Mac device but if it was from a mobile device seems to work better. But so far yet to test a stream game on a faster router if it would solve the issue, that is yet to test.
Hope this helps and lifts your spirit in using your Apple TV with your mac.
Cheers
Karim