you have two seperate lc circuits there.... one is for the actual rolloff, the second is to get rid of a natural peak in the driver/cabinet. My understanding is when these are tuned correctly, that there is a fairly nice, flat impedance curve, but I also heard these were further tweaked by infiinity(read arnie), causing some nasty impedance dips.
I had some fairly trashed walsh speakers in my 4.5's, and instead of messing with them, I put in a pair of infinity beta woofers, both wired directly to terminals on the back of the speaker without using any of the existing crossover for them. I then use an ashley xr2001 electronic crossover, and found 300hz seems to work best for me.
I probably could use some eq on the bottom end, but as of yet have not bothered, it sounds a lot better than the old stock crossover did. the top end is much more detailed and just sounds so much better with the ashley, and I am I guess running 24db slopes. If you play the bass by itself, it really sounds bad, because when it hits the crossover point, it just stops like it hit a brick wall. With the tops driven, they blend quite well.