I haven't used either of them. I played around with Systems C a bit when it was the rage but found that my issues weren't in optimizing some bit of C code with a better opcode rather it was assembling a system with the peripherals I wanted in the places I wanted them.

For a long time I considered soft CPUs a bad idea (the Stretch guys kept trying to sell me on them but since I wasn't really doing things like deep packet inspection I didn't have a good use case, even RAID algorithms on them were better handled by pretty generic DSP type architectures.) However in playing with the Zedboard which has a couple of Cortex A9's attached to the Xilinx fabric I find some interesting things there. If only as a new kind of 'i/o' but that is neither I/O port based nor memory map based (it expresses as memory but it feels different than the memory mapping of old like on the PDP/VAX machines and 68K systems). Could just be nostalgia though.