Well, features like exceptions and classes don't improve performance. You could write the same code as fast in C, even if it would perhaps be more cumbersome and error prone to read and write. You save perhaps development and maintenance cost, but not runtime cost. Features like lambdas don't improve performance either, they rather make the language easier to write and even more hard to read (think of the name of a function as part of the documentation).

In theory the higher abstraction of C++ provides for optimization opportunities for a sufficiently smart compiler. I have yet to see such though.

Write the little bits which need to be fast in C and the gross in a sane language mere mortals can read (e.g. no 'most vexing parse').