Howdy,
Like others have stated, it really depends on what the generator capacity is, how long the run is, what type of wire you want to use.
Standard #6 AWG THHN 90C will be fine at 75 amps (4 wires needed, 2 hots, a neutral, and a ground)
A flexible type wire cord, like a extension cord, rubber coated and flexible and weather resistant. There are some options here. The naming conventions is kinda important to the outside covering and the internals construction.
Standard 6/4 SOOW cord is a bundle of 4 wires sized #6AWG stranded, covered in EPDM Rubber gets you 45 amps
A more expensive way would be with Type W cord. a 6/4 Type W cord is constructed differently than SOOW, it cost more, but is industrial flexible and covered in EP Rubber and gets you 87 amps.
Anytime you start going a long distance, you start getting voltage drop. So a 50ft run is not a issue. You start going over 100ft, you need to watch what your amperage needs are. A 250ft run will need to be bumped to the next larger gauge wire etc...
OK, say a flexible cord is needed from generator to house inlet, rubber coated cord works here. From the inlet to your electric panel, different ways to accomplish this. In conduit, 4 #6 THHN wires works here. Gets you 75 amps. You also can use copper service entrance 6-6-6-6 ( known as 3 conductor wire with bare ground) gets you 75 amps.
Yes, on one of my video's with the MEP-803A and load bank, I was loading 67 amps. I was not loading 67 amps all day long either. That is using 4 #6 awg THHN wires, rated for 75 amps.