Rein, as of today I see 8x8 BT database results between move 8 and 12, based upon a 1 core search, 15 seconds.
The plydepth I reach is 22-24 ply at that stage.
The DB is a 10P DB.
So calculating from move 1 that is 38 - 48 ply.
Assume that after every 4 moves (so 8 ply), 2 man disappear (due to capture).
So a 12P DB would give an advantage of about 8 ply, so than the search depth becomes 30-40 ply.
Knowing the hyper speed Joost Buijs realized, all does not seem impossible...
So I dont think I need to go to a 16P DB, but the proof of the pudding is in the eating.
How many pieces does the end of your PV have in those searches? And what percentage of nodes are from 8 vs 8 pieces? If the PV goes quickly to few pieces, then it might indeed be encuouraging!