i did a little research:

assuming we do actually have 2-ohm speakers here is the attached chart of filtered frequencies

aftermarket fullranges are good down to about 125-150 Hz, so for factory speakers we should be looking at about 175-275Hz filter. This corresponds to a capacitor should be around 289-455uF. this agrees with Max using 270uF to filter alot of audible bass, and others who have used 330 uF, which filters below 235Hz. But i think its important to say the crutchfield bass blockers are a waste because they are rated for 4 (and 8) ohm speakers down to 150Hz @ 4 ohms, so for us thats filtering 300Hz and below, they are 265uF even lower than max's. which seems like it will cut alot of the bass to me. I'm gonna try something closer to 400uF shooting for a 200Hz crossover.