Another anecdote/data point:
I use wireless internet in my home office plus a wireless keyboard and mouse. I trade for a living (but not scalping/day trading) and the set-up seems to work fine. In most cases, as I'm releasing the left mouse button, I see my limit order show up in the NBBO or some other quote screen. That's fast enough for me.
And sometimes as I'm releasing the button my "filled trade" siren goes off (IB TWS) and I get up and do my victory dance. The latter is highly recommended. It forces me out of the chair, which is good for circulation, the back and the neck, and I'm sure my neighbors love it. One of these days, I'll have to get a Cramer-esque buzzer and flashing lights.