Well I love all the extras on the IR3.
I have several and it makes them really easy to set up. Also the thermometer is really handy, if the temperature goes up you may have to re chrono. Rather my gun tells me and gives me a chance to do it prior to getting penalties for a hot gun.
At the end of the day you may be able to get more bps from the Speed, but I get more than enough from my IR3s.
Had a Speed for about a week and sold it. If the IR4 comes with an LCD and all the extras, will get one of those.