The only game I'm having problems with so far is Melee.
Other players usually have around 60-90 ping but desync always happens near the end of the match.
Have you guys tried using the latest dev build? Also, what do you have your pad buffer set to?
Make sure your memory cards are synchronized, make sure you're using the latest development builds.
If you see "Desync Detected by" any player, then, you've set something up wrong, have a bad ISO for one of the players, or are using a setting that is not deterministic.
More than 70 ping is not little much? Because for me, better is less than 45 for playable... I have fiber, my friends have fiber so we get 15 ping :3
Neither ping (latency) nor pad buffer is the culprit of your desyncs. As stated above, make sure you all have the exact same memcard (or better yet, disable memcards and play with everything unlocked using codes), your md5s match for each of your ISOs, and your Dolphin settings are the same.
Yeah, I've played at 300+ ping without desyncs. Theoretically no amount of ping would cause a desync.