What's the Difference 4" Stroker CRANK??

What's the big difference between the lightweight 4" stroker crank:
http://www.ebay.com/itm/201253889755?_trksid=p2060778.m1438.l2649&ssPageName=STRK:MEBIDX:IT And a scat regular cast stroker crank???

Then there are these:

http://www.ebay.com/itm/331369354372?_trksid=p2060778.m1438.l2649&ssPageName=STRK:MEBIDX:IT

http://www.ebay.com/itm/330490891612?_trksid=p2060778.m1438.l2649&ssPageName=STRK:MEBIDX:IT

I realize one is lighter but there is also a price difference. I'm building a mild torque monster 318/390 stroker. The motor will never see anything higher than 5800 RPM, besides I already have a modified 2004R overdrive installed, 1800 stall converter and 3.73 gears in the car so I don't need high RPMs anyway. Just lots of torque from 1K to 5800 RPM. Car will be used for street cruising with the occasional stomping of the gas pedal.

thanks,
Treblig