Old gentlemen in their eighties or nineties, mostly now gone on, have spoken
to me of the fearsomely aggressive nature of the "black Italians"  imported
into the UK in the twenties to make up for losses put down to Isle of Wight
disease.  I don't believe these bees were aggressive when imported, but as
often happens were quickly superseded and the daughter queens, mating with
native stock, enjoyed hybrid vigour which manifested itself in bad temper as
well as increased honey gathering.  This may have created the myth that good
honey gathering and bad temper necessarily go together.
I have noticed that it is the fashion among our North American contributors to
try queens of different races, eg Carniolan or Italian, often on the same
shopping list and presumably in the same apiary.  If one person isn't, maybe
his neighbour is.  I wonder how many of the reports of killer bees are really
down to hybrids or first crosses between European races and nothing at all to
do with Africa.
Chris Slade