Subscription are cheaper than API prices, so probably better to go 2nd Pro sub.

But FWIW, ChatGPT 20x plans aren't available right now, see: https://www.reddit.com/r/OpenAI/comments/1wctjkx/tibo_pauses...

And FWIW, if/when the 20x plan comes out, you can consider getting a Pro 5x plan first to see if you can fully utilize that. Upgrade that second account Pro 20x if you need it. Saves you $100/mo.

Learned this the hard way yesterday. Spent $250 on tokens that ran out after just a day. Meanwhile my $100 sub lasted me a week with the same exact work

It is best to try a subscription instead of the API; subscriptions are always cheaper than the API, regardless of which LLM you use.(However, the additional quota will be reset today.)