Ideally for better SQ cross lower. 60Hz is a good point for sub/midrange at 24db slopes. For rock music crossing higher at 80 will make kick drum have more punch i guess but if you really want that live concert sound, cross lower than that around 60 to give you that chest thumping impact.
If you can fix the null that you most likely have in the 400 to 500Hz range.
It makes sense to cross lower than 80 because when you look at the Equal loudness curves, as you go lower and lower your ear sensitivity to the frequency goes lower and lower. So you want your 20Hz to 60Hz louder than your 80Hz region. If you cross at 80 you won't get the low end impact of whats beneath because 80Hz will be at a comparable level.
Like you said there are compromises. For most two way systems with a woofer and tweeter you normally go with a 6.5inch and a tweeter.You can't alway avoid crossing above the beaming frequency. Even though the tweeter can go down to 2 or even 1kHz in some cases, this dramatically increases distortion and just doesn't sound as good tonally as if it were coming from a cone driver. This is another subject of huge argument. The entire reason that Hybrid and other brands make these wideband drivers is that it will sound best when the most of the imaging frequencies come from one driver. By splitting everything between the woofer and the tweeter it messes everything up. If you go to the Hybrid forums many of them cross their woofers all the way up at 6kHz or 5kHz and this is way above the beaming frequency of their drivers in some cases. This is where the 31 band can come in handy, you can still cross high but tame the beaming of the far driver.
At the end of the day there are just too many issues that are nearly impossible to avoid. My following comments are based on level matching the left and right using the spl meter and pink noise and following up with confirming by ear. The near side in my car has some nasty peaks in the 315 and 400Hz areas resulting in about -6db cuts on both. 500Hz there is a null on either side so they are left at 0db resulting in a boost. On the right side minimal cutting is used for 315 (-.8db) and 400 (-.5db) to get it to match the left. The issue of increased midbass/midrange specifically in the 315,400 area on the near side is very common to many cars. I don't really think install is going to do anything about this. If you have too much in this range it RUINS your midbass impact and kills the realism of bass guitar notes. Another issue that is near impossible to avoid is what happens to tweeters in the 2 to 3kHz region. At least for me 2kHz is 6.5 db hotter on my near side than my right side, 2.5kHz is about 4db hotter on near side as well. This problem is due to the near tweeter being physically close to you not due to axis. This problem could probably be reduced by going with kick panel tweeters but A pillar tweeters are going to show this response. Just wanted to highlight some of the issues that are difficult to fix by just the install.
