if you're a high intermediate to advance, i would suggest a nanoray800, it is still so it'll be quick, and because of your experience you'll be able to make adjustments to the stiff shaft in no time.
My Voltric 70 is 3U, and unfortunately I don't have it with me here in Japan. But I agree, it could work very well for doubles.
I have Nanoray 900 3U already, it should be quite similar to Nanoray 800? All my rackets apart from Victor Bravesword have stiff shaft anyway, no problem handling that. As mentioned above I have recently started strengthening my arm and wrist, now I can already play quite well with Arcsaber 11. Just need to do some more exercise and medium balanced rackets should be fine. The extra control I get from for example Arcsaber 11 compared to Bravesword makes a big difference in shots.