1. Not sure what you mean by "assembly simplicity" ? Both size switches should "assemble" with the same relative ease.
2. To me, the primary criteria would be whether each will be of sufficient size to easily accommodate the switching of your largest engines from one loop to the other without any issues, which generally means going with the larger size.
3. Personally, I like using O-72 switches for the above reason and also, because it allows a closer spacing of the two loops together and saves layout space for other items, like scenery or buildings. However, your particular layout might not need or want that.
4. Are you committed to using RealTrax ? It typically does not rank high on the list of available trackage choices and with MTH going out of business, that may be an issue.
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