The Cisco switch model makes a big difference in whether or not you hit a bottleneck on the stack ring - more than the raw bandwidth numbers will show.
The 3750(G) switches had a much different stack architecture (Stackwise) than the newer StackWise plus on the 3750(X) and the Stackwise-480 found on the Cisco 3850 switches. The 3750 stack will not do local switching - every Ethernet frame going from any interface to any other interface will go across the stack ring. This includes traffic going between interfaces on the same physical switch. Stackwise also does what is called source stripping, where the packet is removed from the ring only after it returns to the source switch.
The 3750X with StackWise Plus and the 3850 switch with Stackwise-480 can do local switching mainly because it has centralized design for all layer 2 and layer 3 protocols. The 3750 uses distributed design for the MAC address table and SPT. There are other inherent reasons in the different designs as well.
How would this affect your theoretical bottleneck question? If you have a large amount of locally switched traffic (servers to database etc.. ) you can hit a bottleneck on your stack's ring before even getting close to your maximum upload capacity on your uplink.
The paper you want to read to understand the differences between these different stacking protocols and which also discusses throughput bottlenecks is the,
Cisco StackWise and StackWise Plus Technology white paper, easily found with a google search. If you search for stackwise plus white paper it will be the first Google search result.