Hot Rods F-1 castor?

My latest project will get an F-1 front axle with quarter elliptics and split bones so I can't adjust the castor after the welding is done. From the conflicting info I found online, it looks like 4 degrees might be the magic number. Anybody have any real world experience with this?

 

I wouldn't go that low on anything. I find that 6 or 7 works well on most any car. I use to run 9 degrees but I'm not on freeways much so I came down to 6.