I am not an acoustic specialist, but nornally what I do just check the rough STC values from these tables and deduction of framing effect by around(5-10dB), and test it! For you case, if you look at the Fig10.17 last case in comparing with your case. I think you will get STC more than 55.
I've seen some acoustic specialists used the software called LMS Virsual Lab to model the whole facades. hope it maybe helpful for you.
Take a look at our Video on Facade acoustics;
Our facades acoustics experts would be more than happy to offer input, if we are able.....