Hi Yanke, and welcome to TPU
RAM is volatile, which means when you start your computer the image of the RAMdisk will have to be reloaded from the HDD. Once it is loaded, though, access will be much faster.
Putting the application itself in a RAMDisk is not going to buy you much. Once the OS loads the app from the HDD it's in RAM anyway. The same is true for the xls files.
You will get better loading times and also write times, but eventually you will have to write the data back to a non-volatile store so you don't lose it when power is shut off.
There are 3rd party, non-volitale cards that will retain what's in their RAM, but they are usually much more expensive than a comparible SSD.
As for calculations, the processor is reading (and writing) everything from RAM already, so a RAMDisk will not help you there as it's using it's working set in RAM and not the RAMDisk. If the file(s) are so large that the OS generates page faults (needs the pagefile) it's going to be using the HDD anyway. The only real way to speed up the calculations is to get a faster processor (or if the application is optimized for multi-core/threading a proc with more cores) or faster RAM (I doubt you would notice a difference with faster RAM as even standard RAM is blazing fast compared to all the other peripherals).
Your best option, as stated before, is to get an SSD. I don't think that an interim/temporary solution is going to be worth the effort.
Just my opinions.
