eddie, learn ya shit before saying stuff
a like for like speaker will distort at the same level, also depends on how your powering it.
if you take a 17cm 100w rms coaxial set, and a 6x9 100 w rms 6x9 set, they will both distort at the same level.
now, if you arent going to put a sub in your car, yeah 6x9s will do the job,
although being that andy has said he is putting a sub in, coaxials are much better suited to the job
and as for the 6x9 covers mid bass bit, your almost speaking exactly the opposite of what is true.
6x9s produce more low bass, hence the reason for using them if your not putting subs in. 17cms are mid bass.