Question Apeks rk3 hd sizing help & boot suggestions warm and cold waters

[Snoegie]

I'm very new to diving and I'm considering buying the Apeks rk3 hds as my first fins and gear purchase (aside from my mask) but am having trouble determining the correct size. I dive in both cold (10c) and warm (26c) areas. My question is two parted:

I am a size 41-42 in normal shoes

1. Would there be a boot that would work in both these climates? What would you recommend?
2. With that boot in mind, what size should I pick up in the rk3?

Thanks!

 

[Wetsuit_]

5mm soft sole boots with size medium

 

[Deezer-D]

I have both RK3 (white) and RK3 HD (orange). I’ve Fourth Element Pelagic boots (UK size 8) and Waterproof B1 in Medium. Both boots are 6.5mm. I originally ordered medium RK3s but they were too tight. Have both in large. The HDs are for use with my just ordered Seaskin Nova so hopefully they fit with the Tec Boots.