Play two tables
Mike,
You are focusing on rake which is only one aspect of EV. 20/40 should be much harder than 10/20 so your profits won't be 2x.
And, probably even more important, you get a massive variance reduction by playing two 10/20 tables. This means that you can play two 10/20 tables with a smaller bankroll than you can play one 20/40 table.
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