The K04 is really a great choice. performance, fuel consumption, driving satisfaction is well worth doing.
I'd go with AWE's or other K04 kit w/injectors, and add a hpfp upgrade from HPFP or APR. It allows extra cash for other things and is the same product. The power from the K04 is noticeable over a stage 2+ even, as my mech has the 2+ and really enjoys test driving mine when he works on it. He even took his wife for a drive in mine because I think he is hoping to convince her to go that direction with theirs. I think on average(AVERAGE) you'll cut 1 to 1.5 seconds off 1/4 mile et's compared to K03 cars. You can easily get up to near 300+ hp with the K04. The stage 3 is geared slightly more toward top end where the K04 will have a bit more punch around town.