It all depends upon at what point do you feel that the print lines are noticeable.
The trouble is that if you have ANY surface tilt, then there will be print lines.
There is a difference between (necessary) print lines due to the layering of the process, versus print lines due to 'jitter' in the print head as it moves from one layer to the next.
In the image below, you can see that there will be "print lines" due to stepping even on a surface as flat as 0.2 degrees, but on the vertical wall, you will get some "print lines" due to the print head not returning to exactly the same spot each time. They're caused by two different situations.
Note: all of the print lines should be significantly less visible on the Polished materials.
As far as a plugin to show you what to expect, I'm not aware of such, but it would also depend upon which drawing program you're using. The other issue at hand is the dreaded "print orientation" topic - at this time, you're not guaranteed any particular orientation, which means what you see as "flat" may have all of a sudden become 90 degrees. One thing you might do is see what the "slicer" option of Netfabb Basic will show you.