And yes, in Gian's system Opus sounds better. It does a much more front to back depth, denser image with flow, more natural tone. But in his system, or the Doehmann + TAD of Tbzc, the GFS sounds different to what it does in Mike's.
So best way for you to answer this is to buy the Opus and send to Mike. Check compared to GFS there as well.
If Opus is better, keep it.
Next, buy the LT and have it set up. Then ask Mike to come over with his Durand, set it up, and see if you still prefer the LT.
If yes, keep it, else it will be snapped up pronto in the used market