Allotments 4 All

I  sowed some Kilaxy cabbage seeds and they have germinated well but they now need potting on.  They have 4 true leaves with two more about to unfurl.

As I suffer from club root on my plot how big a pot could I transplant them in to now?  I do want to eventually plant them on the plot but would like them to have a big a root ball as possible before I do this.

As they wont overwinter I think I need to get them growing quickly.

I transplant all the brassicas into 3" pots, then into 5" pots, then into the ground, we have a small challenge with club root so I don't take any chances  ;D