Transparrent Ref XL vs Opus

Mixing and matching Transparent cables is fine, but the order of your upgrades depends on which Generation you currently own. We just upgraded from Ref XL Gen 5 to Gen 6 and the improvement was startling. If you have G5 interconnects I'd upgrade them first, before moving on to speaker cables.

I believe the Gen 5 to Gen 6 upgrade is comparable in magnitude to the previous upgrade to Gen 5: that upgrade really opened things up with much more air and transparency, with superior dynamics and life.

In the 5 to 6 there is more information and air, again, with bass "faster" (clearer and less smear) and more impactful. 

The improvements are immediate, you don't need to sit there and think about it. I recommend doing an A-A-B if possible, listening to the first product twice before switching to the other. Many times what we hear second sounds better--even if you know the system and music well, there is a certain familiarity and seeming improvement with the second listen. Then, what you hear third (the B) stands out in bolder contrast to the first, whether for better or worse.