Forgot to mention that if you use the software vendors presales support team and one of their Known Good configurations support will be a LOT easier to get from them.

My company decided it wanted a new FEA machine. They decided to stay with the existing software company, so I called up the company and explained the situation and asked for the department that provided pre-sales support, specifically hardware recommendations. Turns out they had a strong bench of people ready to help with that and detailed Known Good configurations for each major hardware company. We simply decided looked at the software licensing costs, the hardware costs and how long our average scenario would take under various software/hardware configs and sized it to handled the existing number of jobs plus expected growth.

We decided what we could live with in terms of how long an average job would take (we decided we could live with 24 hours as an average). We then decided what sort of tradeoffs we could make in terms of hardware (an up front sunk cost amortized over many years) versus the annual software license fees. A little more spent on hardware up front meant we could save on software licensing costs by taking a step down in numbers of processors permitted. We then presented this decision to their presales people to get it vetted and asked for suggestions. In our case we took the suggestion that we archive saved results to our enterprise grade disk array and put the money into Raid 0 SSD's to speed up the overall job time. As always, RAM was the cheapest upgrade so we maxed that out.

Everyone signed off, we took the specs to a local system builder with a good reputation, told them no changes of ANY sort to any component, negotiated a price that included acceptance testing to ensure compliance and made sure they had enough of a profit margin so as to discourage shortcuts. They delivered, we tested, it gave expected performance results, we accepted it and paid them. That system is installed today and delivers the results it was designed for.

I would suggest a similar course for you.
1. Decide on the software first. Make darn sure it will do what you want.
2. Decide on how fast jobs need to be finished and how many per week/month/year to prevent over specing
3. Call presales support to get hardware recommendations
4. Make the decision on hardware cost versus software licensing cost versus number of jobs to be done
5. Do your homework! Understand what you are specing, talk to others, particularly customers.
6. Take your new found knowledge back to presales a few times to make sure you did not miss any improvements and you truly understand what you are doing, you are betting your job on this.
7. Find a builder, local or the hardware manufacturer, negotiate terms. Make sure you leave a decent profit margin to avoid the temptation to skimp.
8. Test, test, test. Confirm all configuration decisions with presales support.
9. Pay 'em and install the machine.
10. Don't forget to follow up to ensure it continues to work as designed and that procedures are being followed. In my case, we checked that all runs were backed up on our enterprise disk array.