Bike Forums - Trick track barspins

Since my 700c front wheel hits the downtube I'm wondering which front wheel to get to clear barspins:
1) 650c
2) 26in

https://cimg9.ibsrv.net/gimg/bikefor...35028e6061.jpg
https://cimg7.ibsrv.net/gimg/bikefor...e3713965f4.jpg

I know I should be looking to get the first option that clears the downtube so as to not affect the geometry of the bike too much, but I'm also looking to throw my barspins without having to think of crank positions - hence why I'm also considering a 26in with a skinny tyre - I suspect finding 26in inner tubes will also be more common.
Which size do y'all experienced fixie fools recommend?

P.S. I'm based in the UK and am having a hard time finding a 650c front wheel online or a 26in that doesn't belong to MTB. Do you know where I could find either of those?

Many thanks