Length of speaker cables

The improvement will be huge. But not because of the shorter length, but only if you use this as an opportunity to upgrade to better cables. That will be huge.

So what you’re saying is that all things being equal (same cables) the shorter length may be an improvement but not a big deal?

Right. If all you do is cut one down I doubt you'll hear any difference. Or put it this way, what little there is will pale to nothing compared to the amp. Whereas you could easily upgrade the cable enough to be an obviously greater improvement than the amp. It all depends on the cable. The biggest impact of length by far is that the longer the more it costs and so the less quality you can afford.

No there won't be an audible improvement. 

As the French Chef says "No diffawrance!". But I would cut them in half for a neater layout.