Why stop at 4?
Personally, I play up to 10 tables simultaneously. It took some time to get accustomed to playing so many tables, but after a while, it becomes a breeze. The one exception is with tournaments, which require a lot more of my attention. So to answer your question, I would 4 table the $50 limits rather than doing only 2 of those tables and then a couple of tournaments.
Best of luck, and feel free to email me with any questions you may have.
The Greedy Gecko
If you aren't winning at online poker, you're doing something wrong.
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