From a cost standpoint, if each switch has it's own dual uplinks, vs. a stack with dual uplinks, you'll need more ports at the distribution level, more cabling between the closet. If you're using copper for the uplinks, both the additional ports and cable runs are likely less expensive than the cost of the more expensive switches. If using fiber, beside the additional cost of the cabling and distribution ports, there's also the additional cost of the fiber connectors (e.g SFPs).
From a performance standpoint, the 2975 provides much higher bandwidth between stack members. This could be important difference if the closet hosts use gig and there's much traffic between hosts within the same closet. (BTW, the client port speed is important, 2975 provide 3x speed ports, but 2960s can be had with 2x speed ports. Assume choice is between 2960s with 3x speed ports too.)
There's a system management consideration, "one" closet switch to manage and monitor vs. multiple switches per closet (alough "clustering" is an alternative).
There's also VLAN management issues. Too complex to address here, but a single (virtual) switch per closet might be better when dealing with VLANs.
