Unfortunately std::deque is hobbled in the Microsoft implementation. Its block size is such that if T is larger than 8 bytes it devolves to a linked list.

And it can't be fixed due to binary compatibility.

https://github.com/microsoft/STL/issues/147

By contrast the GNU implementation has a block size of 512 bytes

Fortunately in high performance systems the times where you actually want an unbounded queue are limited.