Others might beg to differ, but I feel like Len cold pretty much requires being XSY'd with his power voicebank; I find it too weak to use otherwise. Miku solid benefits greatly from being XSY'd with original.
I don't use V5 myself, but I agree with this statement. (Especially since voicebanks with multiple appends take up so much disk space and generally cost more than voicebanks without.
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)
As much as I like XSY, it doesn't quite serve the purpose it was intended to have. Sure, I can XSY Len power with cold to get a combination of the two voicebanks, but if I increase it to a certain amount... the results aren't pretty, so it doesn't really coverup switching between vbs.