Sometimes you can't have the best of both worlds. Yes the Sony is best for gaming because of the input lag but it's an LCD. You will never have blacks of a plasma on your budget. It's a gaming tv , I wouldn't worry about it so much. Didn't you check the S60? It's cheap and good for gaming with the black levels you are looking for. All the stuff you read on the plasma forums it's not necessary, although some panels are more prone to IR for some reason. Obviously if you just game on it for 8hrs / day, everyday you probably will have some sort of IR. So you are better off with the Sony and live with it. I have last year's GT50 and game on it all the time , never had a problem with anything and have an amazing picture quality with the deep inky blacks.
Media room- LG 4K OLED EG9600, Pioneer Elite VSX-90, Samsung 4K K8500, Klipsch Gallery G28's, Klipsch Sub 12, Klipsch RS-52 II, Optik HD cable
Living room- Sony 4K 79XBRX900B, Onkyo RC-360,HTPC, Klipsch Reference R-62II, Rc52II,PS4
Gaming room -Panasonic ST60, PS3, Wii