Every time I've tried it, adding GC to a C program makes it faster. It will increase the RAM usage by a bit, and exactly when pauses happen is less predictable

Every time I've tried it, adding GC to a C program makes it faster. It will increase the RAM usage by a bit, and exactly when pauses happen is less predictable (unless you explicitly trigger a GC in e.g. your main loop), and possibly individual pauses larger, but overall program execution time -- throughput -- increases. Malloc() and free() aren't free, and in particular free() does a lot more bookkeeping and takes more time than people realise.