On iOS, there's a developer feature which lets you simulate packet loss, etc. It has various presets for 3G, edge, WiFi, etc. One of them is called 'Very Bad Network' and has the following (grabbed from the full list of presets here: http://jeffreysambells.com/2012/09/22/network-link-conditioner):
- In bandwidth: 1000 Kbps
- In packet loss: 10%
- In delay: 500 ms
- Out bandwidth: 1000 Kbps
- Out packet loss: 10%
- Out delay: 500 ms
This is obviously not real life evidence of anything whatsoever, but someone at Apple thinks that a bad network has 10% packet loss. Two machines both on a bad connection would have 20% packet loss on their communication (well 19%, I suppose).
I think if you can deliver a reasonable networked game experience under that sort of packet loss, then you're doing fine.