MERV level on home AC filters in South Louisiana

With the dog days of Summer sort of upon us already, what's the MERV level of the air filters for your home's AC?

I was using an 11 level filter geared toward eliminating allergens and odors, but noticed when the temperatures outside got above 90 degrees yesterday, the AC struggled to keep the pace.

I'm running a level 8 filter as of this morning and hoping for more efficiency.

Are thick filters with all the bells and whistles just too thick for South Louisiana in the Summer?