Sam, maybe i mixed up some figures ....
the spin-halyard line is a hollow-braided type (no core)which is very soft and "compressable". These compression-factor is the problem. A 5mm goes down to <3 mm under load while cleating. Normally the type of line used in cam cams is much stiffer (like on your Cunningham or retriever line), compression rate is less.
In case you splice some rope inside your 5mm halyard to beef it up, wear and tear will rise significantly as the strands of this rope are "widened" from each other.