FWIW on my 6th tap I kept the same 1/8" ID lines in and only swapped the non-FC Intertap with the Perlick 630ss (soda water keg @ 28psi, 38deg). Just from switching the tap I could immediately notice MUCH more carbonation in the soda water. Small pour, large pour, back-to-back, waiting 1 week, etc pour doesn't matter. It holds much more carbonation in solution from the line to my glass.
A quick summary of my journey for anyone interested -
GE 5.0cu ft keezer, 1 regulator @ 12psi, ~40deg, fan on lid for recirculation, used for 3 years.
1) Perlick 525ss (3), Accuflex Bev Seal Ultra lines (~15ft) with John Guest fittings.
Extremely smooth pours, small/full/back-to-back no issues. Occasionally needing to lower glass to get proper head on back to back pours
GE 7.0cu ft freezer, 6 regulators @ 12-18psi, 38deg, two fans on lid, used for 1 year.
1) Intertap G1 non-FC (6), Accuflex Bev Seal Ultra lines (~18ft) with John Guest fittings.
Full pint pours quite foamy, about half the glass. A lot of carbonation out of solution in the lines themselves. Fast pour. Direct back-to-back pours were OK, but after left in the lines for a few minutes would pour the same. Very aggressive initial flow and stop of the liquid.
2) Intertap G2 FC, same lines as above.
Basically the same as above, maybe slightly better when turned completely down, but still not great.
3) Intertap G1 non-FC, 1/8" ID EJ Flexelene Silver microbial FXAG tubing, associated 1/8" ID SS tailpiece.
Initial pours were good. All beers took about a week to "acclimate" to the lines, as initial pours had zero lacing. As the keg got down closer to empty noticed more foaming. Direct back-to-back pours were OK, but seemingly after a few minutes to up to an hour later of a pour would be very foamy. If beer sat in the line for more than a few hours/days, it would pour OK on the first one. This was very inconsistent from tap to tap, cleared lines and checked for debris with no issues.
4) Perlick 630ss (6), Accuflex Bev Seal Ultra lines (18ft), same JG fittings as above.
Perfect pours, small pour, large, back-to-back, 1hour wait, days/weeks/etc zero issues on pour. Much more carbonation held in solution from line to glass. No initial foam out of faucet regardless of keg fill. Direct back-to-back pours will need to lower glass in order to build head it pours so good.