There's no huge diferrence between the sound coming out of slant compared to straight one if you're really close to the cab.
On slant ones our ears don't ear much low end 'cause sound from upper cones is set straight to an angle on 30°, this way if you're away 3 meters from the cab you're listening to the full tone of the cone, lower cones are not set straight to your ears and so you don't hear the top end.
Try this on your slant cab, go 5 cm near the cab listen to every speaker and tell me if you hear any difference?
I miced every cone on my 1960 lead and the difference is minimal, as Andy says "choose your favorite cone and mic it!" I did it (right upper cone the best for me) this is true! there's a minimal difference, but there is it!!!
Maurizio