10% packet loss though typically is the threshold of "completely unusable" TCP connections. Depends of course, but 5% I generally think of "severely degraded" (e.g. ssh being almost unusable but still able to get some basic stuff done during a sev0) and 10% being "drive on-location because you aren't getting anything done" territory.
How is it not a modern website problem, if that modern website is being viewed over wireless connections, and follows Google's lead in disabling slow start TCP?