Tai-Shogi (25X25 board)

Micro shogi (4X5 board)

That's not even large :P

Taikyoku shogi is two times as big as Tai-shogi (36 x 36 vs 25 x 25).

That's true PhDP  , however as I understand it , there is considerable doubt as to whether Tiakyoku shogi was ever   actually played....

 Quite Correct. They are also unsure what the rules were. (If it was played)

Tai shogi, however, they are reasonbly sure of the moves of most of the pieces.

Either way, tai shogi is large, even if it isn't the largest.

Here's a link to a video showing it being played ...

http://v.youku.com/v_show/id_XNzc2MDExNDA=.html

It took 32 hours to make 3805 moves to finish the game.