Most vendors seriously over estimate their minimum requirements for servers. 40 GB is plenty for a 2008 R2 server, 60 if you're feeling generous.
You don't get to say "They overstated their requirements," and, when the software actually needs to use as much resource as was stated to be required "Oh look, they're using too many resources".
And no... 40GB is not "plenty" for a 2008 R2 boot drive; it is pretty much the absolute minimum for a couple years worth of service, with a likely space exhaustion, eventually.
An extra 20 GB for 40 servers is 800 GB on tier 0 storage (and yes, for these 40 servers they are required to be on SSD).
This is because of your broken deployment choices, and bad assumptions about OS space usage, not an issue with the software.
Attempting to Micromanage microsoft operating system storage requirements will cost you more time in man-hours, than 1TB of SSDs ever would.
And you're accusing vendors of overstating requirements, while you're suggesting servers require SSD storage for just the boot drive?
Don't you see the irony in that?
Of course servers don't need SSDs for the boot drive. Bloody SATA RAID5 is the most popular storage solution for Windows server system boot volume.
It's simply not true that SSD is needed for system boot drives.
Install the applications or databases requiring performance on SSD, not the OS.