The 8ms becomes a critical issue when running it in line with other digital devices. The human perception of latency varies between people, typically 4-10ms. The majority of people will hit around 10ms. So when buying a wireless, also take into account any other accumulated latency that may be in the chain. This included digital pedals (including modellers) and digital desks for example. Then you have the delay incurred as the soundwaves leave your cab and hit your ears. With some wireless with high latency figures, you are already on the cusp of acceptable latency. Of course, if you are wearing inears, the problem is even more obvious.
Just background information for folks that are researching wireless really - not all wireless are equal, especially when it comes to latency.