Your question is, to say the least, very interesting. With that generic approach, for sure, you will pay a lot of money for whatever is the biggest, baddest machine. It reminds of customers of mine from the past who hired me to just make their system go faster with no specific requirements as to where they had performance problems.
If you really want to get an advice you need to be much more specific as to what your requirements are. Otherwise I would suggest you call your IBM account manager and ask him exactly the same. Believe me, he will be quite happy ...
Best regards,
RealHeavyDude.