This depends a bit on the room, but the main concern is going to be overlapping signals from the APs, which causes packet damage, which leads to slow wifi and possibly frequent disconnections. I'd recommend setting the power on both APs to 1 or 2, and then running the command "show acsp neighbor".
In the output of that command, you'll want to look at the RSSI column and see if you have any values in the -50s, -40s, on up to 0. Ideally we want to see these values between -75 and -100, the closer to 0 we get, the louder the signal is and the more likely we are to overlap our signals. If you do see a value in the -50s-0, you'll want to check the BSSID associated with that signal, and find the corresponding AP to lower the power on that AP.
If you're down to 1dBm for your power setting and you're still overlapping signals, then I'd remove the second AP from the room.
