Thank you all fpr your replies.
I held the hand in a speedball tournament (4 boards in 13 minuttes), so I didn't consider it for a long time at the table.
I struck gold:
(Hearts came down for one loser,
♦A onside and spades couldn't be solved for zero losers.)
Afterwards it seemed to me, that the trick would be to play in the suit, where partner is likely to control the third round, i.e. hold some low honours. (All this assuming you are willing to discard the 6-5 hands.)
It also seemed, that partner would have to have a decent amount of HCP/Playing strength in the major-suits.
I am not so strong in probabilety, but isn't it more likely that partner will have these low honours in hearts, rather than in spades, as he cannot have the
♥A? :genuinely bewildered: (Maybe the difference is insignificant?)