I would say that's a little tight. It's certainly possible if you have no luggage to check in but it doesn't leave much margin for error. If the bus is late temperatures will rise faster than a volcanic geyser! Perhaps booking a taxi half an hour earlier might reduce the chances of a hiccup?

My recollection of security at KEF is minimal which probably means it was quick and efficient. However some of the gates are a fair walk away (10-15 minutes) from the main departure area and I don't think we yet know where BA's aircraft will be deposited. The location of the lounge would be a good indication but I believe that there isn't going to be one!