If I remember correctly, in MSVC implementation if sizeof(T) is greater than 8 bytes then each 'block' is just one element (also blocks aren't contiguous). So effectively, MSVC implementation is useless.

Boost does have a a deque container where you can specify the block size using type traits, but from my experience boost's deque wasn't such a good implementation performance wise.

But Clang's libc++ implementation is very good performance wise and even beat std::vector in some cases.