There's no straightforward equivalent of the concept of clock rate in quantum computing. Quantum computers are supposed to produce algorithmic speedups only for very specific categories of problems. In simple words, quantum algorithms can be represented by quantum circuits which are basically a sequence of quantum gates. To give you an idea of how quantum gates are applied, I'll quote Peter Shor's answer:
Consider an ion trap. The ions represent qubits by using one electronic state as a $|0\rangle$ and another as a $|1 \rangle$. A quantum gate is performed by applying a $4 \times 4$ unitary matrix to two of these ions. This is done by shining a sequence of laser pulses on the ions. It's not a physical device into which two ions are input, in which they interact, and out of which the ions come with their states changed.
Such laser pulses are applied at certain intervals of time. You might consider that rate to be a clock cycle rate of some sort. However, you can't immediately map it to a classical notion of "how many instructions are performed per clock cycle?", as quantum instructions (i.e., the state evolution of qubits induced by a single layer of simple quantum gates) can't directly be compared to classical instructions (e.g., bit shifting). So, your statement: "If quantum computers are so much faster they must have a clock rate which is a multiple of this." isn't quite right. In some sense, they might even have lower clock rates (say, 100 MHz) but perform a greater number of effective (classical) instructions per clock cycle (i.e., per contemporary set of laser pulses). Note that this notion of clock cycle rate will be lower bounded by the decoherence times of the qubits.
More importantly, even here, just like in classical computing, the clock cycle rate isn't the only factor determining the performance. Furthermore, it wouldn't make sense to compare the clock cycle rates of different architectures, say ion trap quantum computers with superconducting quantum computers.