McClaren are definitely making approaches to Mercedes for a supply of engines from next season on. That's the only way they may keep Alonso,whose contract expires this year and he has told McClaren that if there is no improvement by September he is off.
The financial aspects of dropping Honda are considerable. They contribute towards the drivers salaries and supply the engines free of charge. Engine cost alone would be about £11M and then they would be about two races behind with updates.
There is no way of knowing the efficiency of the McClaren car as it doesn't perform for long enough or fast enough to determine.
Vic.