The number 1 best thing to throw at PhotoShop (assuming an x64 operating system and the current version of PS) is more main memory. This reduces PS's need to cache to disk as often.
PhotoShop manages its own temporary scratch files to which it writes image data that it cannot hold in memory. These are best directed to a drive other than that which contains the operating system, applications, and your primary working data storage. It does no good to direct them to a different partition on the same drive: That just makes the OS and hard drive work more to retrieve the data.
A page file stores blocks of data from active memory which have been forced out because of more pressing need for that memory space. Increasing active memory reduces this need. Placing the page file on a drive not containing the operating system and applications often improves efficiency. Page file size is best set to a fixed size based on total system memory installed. (see: setting page file info
ReadyBoost stores snippets of data that are repeatedly requested from the hard drives on the premise that the media used for the ReadyBoost storage can respond much more quickly than the slower, mechanical hard drive. This is very different from the purpose of the page file (although both are aimed at increasing the overall efficiency of the whole system). ReadyBoost is most effective in system with minimal system memory and/or in situations where a finite number of file segments are needed repeatedly by the operating system and/or applications.