Interesting theory - but you are diverting away from your earlier point that 'length of study' is driving women away from the profession. Have you any evidence of this, or even evidence that it does take women longer to qualify than men, allowing for career breaks?
In terms of the exam structure, the actuarial exams are already very modular - imagine studying for 6 years and then taking a 3 hour paper that could literally cover anything! I have little interest in educational psychology but a quick read around the edges suggest that the different exam approaches benefiting one gender over the other maybe just as much down to social reasons (girls discouraged from self-belief in their capabilities in anything other than home-making) as to genuine gender differences. In any case, performance in assessment can be down to many factors so I suspect it would be quite difficult to say categorically that a particular assessment style is more suited to one gender over another. Even it there was strong grounds for this at say GCSE level, I would then question to what extent this translates into professional education where the teaching style is very different (self-taught) and those sitting the exams have made the choice to do so.