I can see why you would be tempted.
I have been curious about Mamou, too. Even though he doesn't look Siamese, I am convinced that he's 1/2, just like a similarly marked cat of ours, with a similar size and personality was. I thought about DNA testing, as well, but haven't for the same reason.
Do you have any thoughts on what breed might give him that look?
Tux is a tuxedo marked cat with white mittens, but is also, coincidentally, the longest, lowest to the ground cat that we've had. Though, he's not particularly lean. He's not heavy, but not lean. I can't imagine what gene that would be. (Even if I felt comfortable spending the $'s on a test, we'd never be able to get a sample from him.)
Thanks for the update!
Love All Life, Thank You For Posting! :)