There are some things to consider. Humans can hear Phase relationships quite easily. Just take your speakers, put a phase switch on one and flip it ... this is the type of thing that introducing latency on one side of a stereo signal can introduce and very low numbers.
When I say I can feel around 5ms ... its true ... me switching on a 5ms delay in my sound causes a mushy, disconnected feeling between my pick and the sound ... its minor at 5ms, but I can feel it.
When I say I can hear 8 - 10ms, that's when I can hear both sources at once. Again, if you take one speaker of a stereo pair and delay one by 8ms you will hear a lot of phase relationships get affected, and a perceived slap delay and shift in the stereo field.
I practice at a low enough volume such that I can hear the acoustic sound of the guitar, its the delay from the acoustic sound to the speakers sound that is bothersome. In a live situation its common to have more legacy introduced by distance and its easy to get used to because you can't (normally) hear the acoustic sound of your instrument.
Cliff made me consider all the things in my chain introducing latency, when I stack them all up vs the acoustic sound of the guitar on my body:
Wireless: 4ms
UA Interface: 2ms
Axe: 2ms
Distance: 8ft (about what ... 2ms?)
It gets into the perceivable range.