Depends what dom traits the parents hold.. Only way to find out for sure is chuck some pollen mate. The line that is more inbred will probably give you more dom traits from that parent in the offspring. Bubba kush is a nice exp of this, pre98 and GHS bubba are 2 distictly different lines.. The kushs' used were dom in totaly different traits. So the results are one beeing kush dom the while the other a bubble gum result.
If they are genetically different your F1's should be pretty homogenious, F3's are where the real diversity in phenos starts to happen.
I know this doesn't really answer your ? but no one can really say what parent is going to do what "FOR SURE" unless you see what parent throws what traits.
But if i had to say my money says the kush is going to lower the flower time, and you will get a more stout plant than the mexi mom, with a kushy,skunky sativa type smell. Could be interesting... If you have time to work it. The afghani will sure add some thing uniquie. Alot of citrus and pine type smells come from afghan lines.. Could make yourself a OG type taste. Breeding is more addicting than growing
the combinations are endless.
Bh.