I've now noticed that I've never had a ball that has been flippy for me. I've had balls that are strong in the backend but all of them have still been predictable unless the lanes really broke down.

I threw a friends Victory Road that he had left yesterday and all I had to do was throw it right and watch it come back shredding the rack.
I'm really liking Roto Grip now since picking up a Soul as I can now cover Heavy to the slightly heavier side of medium with my Rogue Cell and Defiant Soul. I have a Crossroad under those 2 balls but I have it with a smoother layout so sometimes it doesn't have enough punch downlane until the lanes really open up. Could a Deranged fit the bill of being a skid/flip ball or should I just look at getting a Fire Road or another Crossroad?

Totally Defiant.  As long as there is a dry spot on the back ends, this ball will ignore the heads and come off pretty strong off the spot.

You cant go wrong with the Wrecker.

Hy-Road Pearl,... boom. There's nothing on the market like it and nothing on medium oil that can attack from multiple angles like it.

Here are some good choices for strong backend reactions . . .

Asymmetric Cores
o Totally Defiant - As long as you have dry backends, it is awesome. 
o Defiant Edge (also cheap nowadays as they are discontinued)

Symmetric Cores
o Hy-Road Pearl - Strong but smoother because of symmetric core
o Wrecker - I struggled with mine and ended up trading it out [sorry Billdozer :-) ]   
o Fire Road - Under-rated and never really took off in the market. But, it is also cheap nowadays as they are discontinued.

BTW, my favorite layout for max. backend reaction is somewhere around 65 x 5 x 30 (pin up).

And, a good driller can also make the most of the layout to accentuate the asymmetric core for max skid flip.

If you want big backend try a Motion Hole. WOW!!!

I was afraid to MoHole my hyroad pearl cause it's already pretty long. Gonna MoHole something tho. Was so so on a used raw hammer jacked but don't think that was the best choice!