Bought mono blocks, now spkr cables too long

Since electricity travels at nearly the speed of light. Its exact value is defined as 299,792,458 metres per second (approximately 300000 km/s, or 186000 mi/s). The only reason to shorten the cable is cosmetic. If you decide to go that route, hopefully, you can sell to someone else after you compare and keep the one you like the best. 

Cut them. 
 Have nice 8ga speaker wire, barely fits in my counterfeit Nakamichi plugs!

   Cut to fit. My 8ga are about 1.5 feet. Amp to speaker. 

@tom6897 What length of cable matters? When does the speed of light argument run out of steam? 20 feet? 500? 5miles? 

So long as the cables are shielded, coiling is not a big deal.  Huge problem with unshielded cable.  
You make a good point though that shorter cables are far more appropriate with mono-blocks. 

Get them cut to desired length as others have said and terminated properly. An 8ft pair is probably more common than a 12 ft so can probably sell the longer portion more easily.