In this contribution iteratively detected spatial division multiplexing is investigated under the constraint of a fixed data throughput. Existing bit loading and transmit power allocation techniques are often optimized for maintaining both a fixed transmit power and a fixed target bit-error rate, while attempting to maximize the overall datarate, albeit delay-critical real-time interactive applications, such as voice or video transmission, may require a fixed data rate. As an alternative design option, in addition to sophisticated joint bit- and power loading, in this contribution we invoke both coded modulation as well as channel prediction and identify the most beneficial number of modulation signalling levels, while minimizing the bit-error ratio under the constraints of a given fixed throughput. Our performance results show the superiority of bit-interleaved coded modulation using iterative decoding (BICM-ID) against turbo trellis-coded modulation (TTCM), regardless of using...