so basicly the lexus afm would be a good upgrade if combined whith lets say Rc injectors flowing at least 550?

Changes in fuel need to be proportionate with changes in airflow. The Lex AFM only works with injectors flowing around 550 (unless you have other means of adjusting fueling). 660cc/min = too much; 440cc/min = too little; 200cc/min = way too little; 600cc/min = still too much. The 550's aren't quite perfect either, the mod relies on closed loop operation to trim low load fueling.... but it's close enough.