5'4 or 5'6?

I have been surfing a 5'6 Spitfire for the last year and love it. I am considering sizing down to a 5'4 and wanted to hear people's opinions on size recommendations.
Newer to surfing and have been slowly moving down in board sizes as my skills have improved. 5'4, 140 lbs., low intermediate and constantly improving, surf SoCal (knee to head high).
Still want something that paddles well and catches waves easily in the knee to shoulder range but also want to take my surfing to the next level while continuing to have fun.
1) What size board would be most recommended given my weight, skill and desire to improve?
2) What sort of perfomance characteristics could I expect at my weight and skill level if I did go with a 5'4 versus my 5'6?
3) If I went with a 5'4 would it push my surfing and help me improve at a faster pace?