FRAME THICKNESSES

I WAS WONDERING WHAT THICKNESS OF BOX TUBING TO USE ON FRAME RAILS. WHEN YOU SEE CUSTOM MANDREL BENT RAILS FOR HOT ROD AND DRAG APPLICATION THEY ARE ONLY 1/8" THICK WALL. WHEN YOU HERE GUYS TALK ABOUT BUILDING FRAMES AND STEP NOTCHES THEY TEND TO USE 3/16" WALL FOR MINI AND 1/4" FOR FULLSIZE. I UNDERSTAND THAT THE THICKER THE METAL THE BETTER V GOOVE CAN BE CUT FOR WELDING TOGETHER. SO MY QUESTION IS FOR BACK HALF AND FIREWALL BACK FRAME RAILS WHAT IS THE BEST THICKNESS FOR MINI AND FULLSIZE? WHAT THICKNESS WILL HAVE NO FLEX AND ALSO ON FULLSIZE WITH 400 OR MORE HORSEPOWER WHAT IS THE BETTER MATERIAL?

This exact question has been addressed recently on at least 2 seperate threads. Do a search for them and they should answer all of your questions.