The only advantage to having the 400W + SL30 is that the SL30 allows you to monitor both the back-up comm and nav frequencies. If that is not important or you already have a com2 then go with the 430W. Less wiring, less hassle, and probably about the same cost. For someone like me that already has an SL30 and no IFR GPS the 400W is a good fit as an add-on unit especially since I do not have another com radio. Actually, on second thought I'd probably just add the 430W and use the SL30 as my com2.
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