4th order high-pass filter on a DSP: standard or biquads?
The two solutions in a floating point implementation are assumed to be identical, with the two BiQuads being a factored version of the standard difference equation. The BiQuad is the better way to go for fixed point as you isolate two 2nd order systems and in doing so will be easier to keep stable under variations due to the quantization involved. 

For more details on this, see the responses to this post:

How does cascading biquad sections for higher order filters work?

and

https://en.wikipedia.org/wiki/Digital_biquad_filter

Note too for those less familiar: cascading two filters is the same mathematically as convolving their coefficients; multiplying two polynomials is done by convolving their coefficients. The transfer function for filters is described by polynomials so it is all the same thing; a 4th order filter can be factored into two 2nd order filters.