How would rear 1/4 elliptical setup work for mild prerunning, or would long leafs be better?
:usa:

fine as long as you set it up right. it is just a suspension, you would have to tune it right.

Yes they can. Many fullsize class 8 race trucks used to use the 1/4 elliptic setup. It all depends on how you set it up. Long leafs will be simpler and easier to setup. Regular leafs can easily cycle over 18" of travel. Call Deaver Spring they can hook you up and/or offer some great advise. Good luck. Take lots of pics.

Is it the shocks or the springs that make the biggest differance when soaking up bumps at high speed?

Combination of shocks and spring rate is what makes it all good.

Exactly what Monkeyboy said. Good springs and shocks are essential. You need a soft enough spring to cycle all that travel, but it needs to be thick enough (i.e. many leafs) to prevent axle wrap. But for the most part leafs are for ride height and the shocks do all the damping (compression/rebound). That is why you you will see most hardcore prerunners with Bilstein, Fox, King, Sway-A-Way, etc. shocks because these shocks are designed to take that kind of abuse.

I am not looking to build a hard core prerunner, I was just thinking about building a 87 strait axil 4x4 toyota pickup that I just picked up to play around at our local sand dunes. I would like to be able to soke up the woops.
:usa:

I didn't mean to say that you have to be a millionaire to build a prerunner. A very capable prerunner can be built on a pretty tight budget. If you can have some shock hoops made for the front and the back with the proper springs and shocks you can have a serious prerunner. It for the very tight budget bilstein 5100 shocks (about $50) can be modified to be revalved and recharged just like its big brother 7100 (about $150).