"HDD added to suit". Not all gamers want an additional HDD, they may already have a big one on their current PC with all of their Steam library, and may want to just transfer it over.
And if I offer the usual 1TB HDD in the base config, some people want a bigger one, like 2-4TB.
Edit: Anyways, enough about selling the PCs, what about the config, does it make sense to do this?
I've got a couple of friends that might be able to use these PCs too. Something to consider (giving them away. Course then my upgrade won't be "free - as in beer").