Can someone tell me the real length of Omega Nato Strap ?

Yep you need the 20mm for your Speedy. So the reason one Bond strap costs $200 more than the other, is that while both straps are identical, the Bond version has a different shaped tang buckle, and most importantly has 007 stamped on the keeper near the tang buckle. The regular one has no 007 branding. The Bond version costs a very large licensing fee on top of the cost of the strap, hence why the greatly increased price.

The hardware is also titanium on the Bond version... but the licensing is a bigger factor than the metal, titanium isn't that much more expensive than steel.

Size wise, they have a very broad range of hole locations, so they fit everything from the smallest wrists a regular length OEM Omega strap would fit, all the way to the last hole on the Omega Long-length straps, hence why there is only one size. Unless you're a Tour de France cyclist or Bruce Banner, it should fit.

I just checked two and they are both about 300mm. I also typed "how long is an omega nato strap" into google and Gemini said "300-310mm" and that there are variations depeending on model number.

Just to mention your local boutique if you have one will stock them and let you try them on in store, they’re pretty good about stuff like that and if you go in wearing an Omega they’ll want to help you out with that.

uncut certified 😁