I have experience with both the 45" and the 52".
I had a 45" on my ZX190 and it worked great except when both of us were fishing on the back deck in windy weather. With two people back there the bow would come up higher and the TM would come out of the water more often.
I now have a ZX250 with the 52". The added length keeps it in the water more. I have fished in shallow water (1.9 ft on the fish finder) without hitting the prop. So far I'm happy with the 52".