Has anyone averaged more than Muttiah Muralitharan's six wickets per Test?

Sri Lanka scored 345 in a recent one-day international, without anyone hitting a six – was this a record? asked Daniel Stockill from South Africa
Sri Lanka amassed 345 for 8 against West Indies in Hambantota last week without the aid of an individual six. That did break the previous record, which was England’s 333 for 6 against Australia in Sydney in 2010-11. There have been four other ODI totals of 300-plus without an individual six, one each by South Africa (321 for 8 v Pakistan in Nairobi in 1996-97), India (309 for 5 v Australia in Kochi in 1997-98), Sri Lanka (307 for 6 v India in Colombo in 2009) and Pakistan (302 for 9 v India in Centurion in 2009-10)…