Am I too big for a planet x track?

Ha, mine's 835mm on my 66cm Cannondale :)

Do you know what the biggest PX track frame is?

I imagine there's more room in the post for adjustment but how high you have yours in relation to the frame is about as high as I'd want to go. I'd prefer less post out.

58 is the biggest, but i reckon the post goes up to 850 (which would look rather silly)

The BB to saddle rail max on a 58cm is 880mm, 860mm on the 56cm, 840mm on the 54cm, so leg length wise you could fit a small Max.

Max you would fit a large one fine with a long(ish) stem.

Robyn, if its for the track, you would need the 56cm medium, the 58cm large will be tall long in the seat tube.

Adman, on here, one of their team riders, is probably about 6ft 3" and riders the 56cm. They are designed to have a lot of seat post showing.
The minimum inset is 20cm, any less and it won't clamp properly.