Macro-intense projects, desire screaming-fast PC and/or strategy, please advise

Hi all. I'm a university researcher and I do some pretty intense value of information (VOI) simulations for a number of my projects. Typically these involve loop-within-a-loop macros that can add up to ~10 to 100 million total simulations, taking anywhere from an entire day to a week or more to perform. I am pretty well-versed in efficient macro-coding at this point and don't think I can squeeze much more speed out of my current codes. And I am well aware of the limitations of Excel for jobs like this, but we choose to use Excel because (1) the people we build the models for are familiar with Excel and generally have access to it, and (2) programs like R or TreeAge are the opposite of point (1). So yes, I'm stuck with Excel.

My department has given me the ok to purchase a suped-up PC to do these analyses for us instead of each of us having to sacrifice our personal PCs for the duration of the algorithm. I've found a few threads around the internet with discussions like this but I was hoping to get fresh information. Is there a build or strategy out there I should know about? For instance, I know VBA only allows one procedure per PC at a time, but is there some new cloud or multi-user solution out there? The thinking being in case two or more of us want to upload and run our projects at the same time.

If the answer is simply 'you're screwed', then what's the best PC and/or processor for single jobs? But I'd love to hear some creative solutions as well. Thanks for any and all advice in advance.

Bump up the jam