I have 20s v.2 and a Studio-CC crossed over at 60. The added bass across the front adds a greater depth to the soundstage. It also helps tighten my PS-1000 and give me richer deeper low bass.
You will have to watch that you do not get any bass nodes or cancellations in your room because of the added bass sources. If so, stick with 80.
When I owned my 40's I used a 65 crossover with my EAD Ovation+. Prefered it to 80. YMMV, and your ears too.
Now, I still use the 65 cross with my Von Schweikert LCR15's and VR1's. Just sounds tighter, fuller. Yes, speaker placement is critical for this, as B mentioned above. But it adds more punch, if you will. Hsu VTF-2 for sub.
Like BrianWoerndle I use 20's and cc version 2 for the front/center, but I cross at 50hz. the lower you cross at the more muscle (amp power) you need. If your using a receiver to power the 40's then I reccomend 80hz also.
It doesn't matter how powerful your amp or receiver it depends on where your speakers starts to roll off.
The 40's could be crossed at 60 with out much problem, 80 works too. Actually all of your speakers you mentioned can be crossed at 60 without much problems.
A quick way to figure out what to cross your speakers at is take the +/-3dB low frequency, add 10 to it then go up to the next crossover point, that is a good place to start.
Try both see what you like best either should work without losing anything due to where your speakers starts to roll off.