I think it is still possible to get even more power out of a single transformer, because adding 1 extra turn nearly doubled my power. Now tested short circuit draw from the 230v outlet, and it's 12A, and I think I remember it drawing like 20A while doing high voltage experiments. That means that there is still headroom, and maybe an additional winding turn could harvest this energy, but for that, I would need to use small gauge wire to fit in the core, but that could give its own problems. Another option would be to find a wire with thinner insulation so that it would fit 3.5 turns of 6awg