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It is hard to tell a priori which layout will be optimal. Luckily you don't need to. Try a couple of layouts and look at their timing (in simulated years per day or SYPD) to figure out which is fastest. Keep in mind that timings can vary (a lot!) from run to run, so you may need to run for a while or do multiple runs with each layout to get accurate numbers. CESM recommend 20 day runs without saving any output or writing any restarts (because I/O complicates timings and is best handled as a separate optimization exercise). For ACME and for high resolution runs, 20 days is impractical and unnecessary. 5 days (or even 2 or 3) should be good enough to collect data for determining reasonable layouts, especially given the higher frequency of coupling between the components. See the PIO section above for more discussion about run lengths and experimentation strategy.
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