Yesterday, I reworked the code responsible for transmitting serial data from the dexter board. I haven't tested it yet on real hardware (just the simulator) but it should be a big improvement over the previous code. It should achieve close to maximum throughput _and_ it can be disabled during timing-critical sections of program flow. Only thing that remains is testing it on real hardware.
Oh and my JTAG debugging pins should arrive today some time so I won't have to rely on the simulator much longer.