To your first question, I assume 4 seconds per 100m faster than you would swim in open water if you have a good flip turn, especially over longer distances. The factors contributing to this are
a) flip turn - I assume about 1 sec/100m, depends on your turn speed
b) push off/rest - pushing off the wall is the fastest you will move in the pool assuming you have a decent streamline. You also get to rest your arms for a few seconds. Compare the number of strokes you take for 100m in open water versus in a pool, I guarantee you are taking at least 10-15% more strokes in open water, which fatigues you over time. Imagine that you could stop pedaling on your bike for 2-3 seconds every 15 seconds - that is the effect of a turn in the pool.
To your 2nd question - sure it will, if all else stays the same.