@Ili0 – High alching is not only in efficient, it is costly. It is the last thing you want to be doing. If you want to sit still, then cast superheat item on iron ore. It has lower xp per cast, but you can cast the spell faster, making it much higher xp per hour relative to high alch. The price of nats is relatively stable, so that alone should tell you that it isn’t a very good option (as no one is doing it).

Iron ore on the other hand has jumped up, so if you want to do it buy now. The xp for super-heating will also go to smithing and magic, giving you bonus xp in two skills, and giving you some serious potential XP in 4 more skills if you make the iron bars into darts attach feathers and then use to range a slayer assignment after the bonus xp weekend is over. You will find (even with expensive iron ore), that your cost in terms of gp per xp is extremely low if you utilize your resources to the extent that you can.

Instead, you chose to make simple fundy trades that averaged 4% twice a day. You turn that same 6m into 8,211,414. That is a 37% profit. Stick to daily flipping. It will outpace any other form of trading in the long run.