There is a noticeable difference between 8 and 9 PS, however, the change from 4 to 5 athletics feels VERY significant.
27/12 was my first 1h build, then I respecced to 24/15. You're able to circle around opponents better and most builds can't backpedal against you if you are moving forward properly.
27/12 definitely isn't that bad, though, especially if you are comfortable in lighter armor. 24/15 is usable even in medium-heavy armor. 4 shield means you will get hit around slightly more, but it's more annoying that you can't pick whatever shield that's lying around.