It won't work because all light armor sets (except r8 armor) are having the same -interval stat from set bonus which doesn't accumulate if you are having 2 of them from different light armor set bonuses. On the other hand you will receive full set bonus even with mixed light armor gears (so -0.05int, +10 def and +10 atk levels).
The only way to have faster attack speed would be mixing your armor with 2 heavy armor parts (not really worth it), or 3 r8 parts (they all are using different -int stat).
I hope I explained it clear enough.