My view has always been that adding in the Soprano Choir to the Vienna Choir mix would seriously imbalance the choir sections and make the whole thing soprano-heavy. Bear in mind that the Vienna Choir already has 16 sopranos, as opposed to the 10 altos, 10 tenors and 8 basses, so the last thing I personally would want to do would be to add another 16 sopranos. If you're after a very high, bright sound, then perhaps go for it, but otherwise, I myself would not do so.
That said, Paul is doubtless right, that the two sound different, so there are probably situations where the Soprano Choir sounds better instead of the Vienna Choir sopranos (though the Vienna Choir sections were all recorded with working together in mind, whereas the Soprano Choir was built as a standalone - as far as I know). Also, I have not tried them both together, it could be that I am completely mistaken and that the enormous combined soprano section sounds great.
Pyre
AMD Ryzen 7 3700X 8-Core 3.59Mhz Processor,
64 GB RAM,
Windows 10.0.19045,
Cubase 10.5.20,
Sibelius 7,
VEP 5.4.16181,
VIP 2.4.16399,
Symphonic Cube, MIR Rooms 1-5, Suite, Choir, Organ, Imperial, Solo Voices, Dimension Strings, Historic Winds, World Winds