I too own the Apeks RK3 in white and black but find the XT to be a better all round fin.
Agree. I like the Apex, certainly more compact, & alittle lighter. They took a couple of dives to get used too, and when I use my XT's after a break they feel like stiff planks of wood. But in current when I need to kick through it, nothing compares with my XT's
I can drive through the water even with a slung 80 by my side much easier and faster than most other people, which I put down to the XT's rather than my skill or fitness