and the chip seems to operate at up to 80MHz, and I can't get Serial data to it at 40Mbit/s
True but you don't have to operate the chip at the maximum clock speed you can use any clock speed you like providing it is slower than 80MHz.
Also, is there anyway of adjusting the clock signal?
You write code to make the clock signal, using digitalWrite to place the clock HIGH or LOW.
There are 8 parallel outputs on it, does this mean that I would get this output?:
or would it be this:
It depends on how you write the code that feeds the shift register.
Using the shift out function you can decide by one of the parameters (MSBFIRST or LSBFIRST) Where MSB is most significant bit and LSB is least significant bit.