As photography depends on tedious calculations nowadays (the replacement for darkroom work) you need to have a computer that does the work in reasonable time.
The larger amount of data you have (e.g. directly related to more Megapixels) the more computing you will be doing.Double the MP-number while you stay on the same computer hardware and the computer will need double the time to perform the same task – given a computing intensive task like rendering a RAW file into a displayable version (RIP).
Now, reading that data from disk is one factor, here are some insights that might help make decisions:
… it is a slightly old article, but will still give a correct “picture” of the choice of hardware.
Related: Hybrid drives and the options…http://www.pcworld.com/article/2025402/ssds-vs-hard-drives-vs-hybrids-which-storage-tech-is-right-for-you-.html
… more to come.