I assume there's no dispute that Sylvester McCoy is the shortest? (Although, if Patrick Troughton turned out to be shorter, it wouldn't surprise me.)
I dunno. Considering it's bad lighting and they're all out of make-up, I think they look fine. Except Tennant looks... different. From some angles he looks right and from others he looks like the grand prize winner in the David Tennant lookalike contest. It's especially surprising since Smith, Darvill, & the guy that plays Sgt. Hathaway on Inspector Lewis
all look unmistakably like themselves.
BTW, I didn't know Billie Piper was dating Sgt. Hathaway!
As for those early photos of Tennant & Smith together on the set of "The End of Time," I think it's really mind-blowing just how young Smith looked back then. He still looks young now but now he looks like a young adult. Back then, he kinda looks like an eager young teenager who decided to put on Tennant's suit & make a fan film.
Speaking of Tennant & Smith & fan films, there's this fan film out there called "How to Stop a Time Lord." http://silverwolfpet.com/doctor-who-...op-a-timelord/
It's quality is very fan film-ish in places (as would be expected) and all of the actors have very thick foreign accents. However, the movie does an excellent job of capturing the spirit of the show and what a Tennant/Smith crossover movie might look like. (I'm especially impressed with how the actor playing the 10th Doctor was able to absolutely nail so many of Tennant's mannerisms.)