Q9450 if you can get it for $300 since you won't OC.
Q9300/Q9400/Q9400 are really close together, so the difference in performance should be very small.
The best value would still be Q6600 and XIGMATEK with OC.
Best value is the Q6600 when OC'ing. But for some of the video work he is doing a Q9300/9450 might be a better choice since it has SSE4 which will start to expand into programs soon and give those chips an advantage.