As far as I’ve heard the X3 will only fit unprotected 26650’s. So a 26700 won’t fit without any modifications.
The X3 is a very nice light, with your choice of host it’s like Chickendrumstick said, it really depends on how compact you want it to be.
Another option would be an Eagle Eye X6. It’s slightly smaller than a C8 but it has an excellent thermal design allowing it to dissipate heat much better than lights similar to its size. With a dedomed xml2 at 5+ amps you could achieve over 80kcd.
Here’s a review.