1/4" line should restrict about 0.6 psi per foot, and you're pushing at ~10. A 4' line will make the beer foamy weather it is homebrew or a commercial keg. Get some 3/16" line, that restricts more like 2 psi per foot.
Those should be about 0.2-0.3 psi/ft and 0.7-1.1 psi/ft, respectively.
It depends on the source and material. micromatic says 3 psi/foot for 3/16" vinyl, morebeer says 2.2 psi/foot for 3/16" vinyl. micromatic also says 0.5 psi/foot for 1/4" poly, 0.3 psi/foot for 1/4" barrier, and 0.85 psi/foot for 1/4" vinyl, while morebeer shows 0.65 psi/foot for 1/4" vinyl. For all we know it varies by manufacturer and lot, not just material.
You could do some tests if you trust your pressure gauge. Get a 10' section, hook it to a corny, and run it as straight up and down as possible. Account for the static resistance at 0.5 psi/foot of elevation, then slowly apply pressure until water is coming out the top. The pressure, minus 5 psi (0.5 psi/foot * 10 feet), divided by 10 feet of tubing gets you the resistance per foot. So if it takes 20 psi to get water to the top, you've got 1.5 psi/foot resistance in the line. It will read slightly high because of the poppet/fitting it has to run through, but you could account for that with a second test with a longer tube.