It's different for each game. There's no restriction on texture resolution in fsh itself.

But usually there are limitations in game's loading engine. For example, in FIFA 07 it's not possible to use textures higher than 2048x2048 and not recommneded to use textures higher than 1024x1024. But I don't know much about Rugby games. Here I used 2048x2048 and it worked. But there may be a limit of total memory which is allocated for all textures (there's one in FIFA 07), so it may work with one texture but won't work if you have too many.

As for polycount, there are also different limits, but OTools is able to split mesh into multiple meshes in order to fit these limits.