Going a little heavier with a light plus on the G is fine, not weird at all.
As for mixing Pistoy and Lyon, personally I'd do one or the other- meaning both Pistoy or both Lyon, but that's just me. There's nothing wrong with mixing the two if that's the sound you're going for- lots of folks do it.
As for sustain, clarity and volume- in my experience they are equal- they are different "flavors"- but neither has an edge in the characteristics you are asking about- as long as you are talking pizz that is. IMHO Pistoys are superior arco strings by a wide, comfortable margin.
You can't go wrong with any Gamut string though, they're great!
That's my two cents, hopefully some of the other Gamut heads will chime and offer their opinions.