I guess if you "Need" to watch the weight factors... the aluminum is 3x the cost of standard copper alternative.

A 20' run of 4ga copper cable is about 3.5-5# depending on style.

Even though the alternator is rated at 60A, I doubt that there would be a time when it would actually need to supply that current. I used 8ga from front to back (at least 15') and had minimal voltage drop when checked and 14v going down the track. Use 6 if it makes you feel better.

I use 2ga for everything, positive and negative side. IMO that's plenty as long as the system is done correctly and the components and starter aren't junk. The big stuff is heavy and harder to work with. Once the engine starts, it's just along for the ride.

I'll add that I use welding cable exclusively which is more efficient than battery cable. Battery cable may need to use a larger size. 10' of 2ga welding cable weighs just under 3 lb.

I have gone stupid crazy trying to keep the weight down in my new car. Started with the care itself, a carbon body, carbon brakes, lightweight wiring, lithium battery, last piece is trying to convince myself I need $4500 in rear wheels...It has truly become a sickness for me....

LOL.. my hands dont look anywhere near as good
as my wifes.. she took the pic... I put those
lights in the Rampage.. the race car only has a
single rear light(thats all that is require)

Just bustin ya Mike but they do match...........

#6 stranded for 60 amp alternator.
I run #4 welding cable for a 140 amp alternator.

Its not so much about voltage drop. You drop voltage you have an overheated wire. Next thing you know a break in insulation and risk of fire.