Your router would also have to have the ability to use 3 antenna or it will just use 2. They transmit overlapping signals and although in theory you get more speed from each antenna the extra is less and less...otherwise you would see routers and cards with 100 antenna.
How well any wireless works will be much more affected by how your house is built and the neighbors using wifi around you. Performance is unpredictable but it will not perform even close to a ethernet cable in most cases. I would consider powerline networks if your primary use is online gaming, they tend to have more consistent latency than wireless which is subject to random interference