Potentially a pillar mount gives the furthest distance from listener to the tweeters.. short of kick panels and legs blocking them (mine do)...
Aiming across the dash could work quite well for tweeters with very wide dispertion... Aiming at an angle is good too, but some tweeters sound better off axis than on!
8" midbass in MY mind is not ideal, because the tweeters would have to go LOW to give a good response (again, in my mind)... this doesn't happen in all setups, however the best setup's i've heard have 6.5" mid's, i've heard a few 8's, and while they kick/hit well, we have subs for that
Aaron

I have heard several 8" and tweeter combo's and to be honest, they had one thing in common, a not quite right midrange. I have had a Dyn 8" and Esotar on the dash of the old Echo and while the midbass made your eyes water and the top end was stunning, the midrange was a bit cardboardy and flat. It was by no means bad, but changing from a 6.5" over to the 8" the difference was imediate and obvious. maybe a different combo of 8 and tweet may work better as many home audio set ups use exactly that driver array to good effect.

my idea was based on home audio 8" midbass. The 8" midbass is DLS. Anyway, i listen to all sort of music, but female vocal is very important to me.
Guess i stick with 6.5" midbass.
maybe i can stick a 2"-3" midrange and tweeter at the A pillar?...mmmm

I run 8inch midbass with horns. As long as the tweeters can play down to 2000hz and the midbass drivers aint subs then it should sound extremely good.