ICS all the way you will get better FOC and why not go for it if you can even if its only a small improvement?
I have both these shafts and prefer the ICS, just because of the lighter weight per inch of shaft. I do shoot a heavier and stiffer spine and get 22.3 FOC with them while only around 17-18 with the Heritage. 54# @ 31" centershot static recurve
A very rugged shaft too when footed- the ruggedness factor is mute unless you shoot into rock and/or steel.. I know, I have shot both a lot into hard objects. and the Heritage does win the concret, steel, rock contest.
I didn't apply for a rock tag this year however...
Joshua