Acoustic/ Thermal insulation trade off

[Nye]

I think I'm going insane trying to understand how to layer up my refurbished vaulted ceiling. The issue I guess is I am trading off between these 3 things:

 

Acoustic performance (I have a train line at the back of the garden in a city)
Thermal performance (I will be using a heat pump so want to get the U value down below 0.18)
Ceiling height (Roof pitch is around 30 degrees and ive already lost some overhead height with wet underfloor heating)

I'm currently thinking along these lines (from outside to in):
 

1. Roof tile
2. 25 mm Battens

3. Breathable membrane draped 10mm

4. 15mm air gap in 175mm rafters at 400mm centres

5. 150mm rockwool slab insulation between rafters

6. Tecsound 10 mass loaded vinyl 5mm

7. Vapour barrier

8. 50mm PIR in an unbroken layer

9. 50mm battens, space between filled with 50mm rockwool slabs

10. 17mm resilient bars to create service layer, non ventilated air gap, and decoupled ceiling

11. 2 layers of acoustic plasterboard (25mm total)
12. Skim coat

That should give me a build up of 150mm and allow for recessed ceiling lights that won't interfere with the PIR layer. The tecsound further back will also counter act noise leaking through the ceiling lights I hope.

But All the U value calculators I have found are very limited, even within the manufacturers range of options. And I can't begin to calculate the acoustic performance. It feels like I'm throwing grass into the wind and hoping for the best. I spoke to a couple of architects who seem to have their preferred methods (usually double plasterboard and as much PIR as can fit).

Does anyone know a better way to do this ?

Thanks