what do you think? I want clarity and sustain
how are split sounds?

Honestly, I didn't like the Crunch Lab but the Liquifire is one of the best neck pickups ever. I'm probably ordering more.

I should also add that I'm no clean tone or split sound expert, but my main guitar is wired like this:

1 - bridge full (it's a Super Distortion)
2 - bridge split
3 - bridge and neck split
4 - neck split
5 - neck full

and the only split position I find useful for clean sounds is neck split.

You could try dimarzio wiring for two humbucker. I did it on my other guitar (TZ and Paf pro) and like it. It has positions 1,3,5 as you'd expect with full humbuckers, but 2 and 4 have split inner and outer coils in parallel. Nice for clean.
And I do like the CL. It's a very transparent pickup but still powerful.

Do you find both humbuckers in parallel useful?

No, I don't find it useful myself. I'm simpleton, separate bridge and neck pickups are enough for 99% of stuff I play.
The middle position is like les paul, that's why I said as expected, LP is kinda standard for two humbucker guitars.
Cheers

I would like to have a 4-position switch and use it as bridge / bridge inner coil / neck inner coil / neck!

Better yet...

Bridge
Bridge inner coil
Neck/Bridge inner coils
Neck inner coil
Neck

That's how the switching is on the FR1620. http://www.ibanez.com/ElectricGuitars/model-FR1620

I think it would be more useful than the standard Ibanez 5-way. I really only use 1(bridge), 2(bridge/neck split), and 5(neck) positions on my RGs. The other 2 are pretty useless for me.

That's how my main axe is wired up!