I did some non-scientific testing with this last week and, at least for my problem (brute-forcing RC4 keys with relatively small numbers of long-lives threads,) threads and go routines were approximately equal in terms of performance with goroutines very slightly faster (around 5% or so.)

I have another test I'm running with the same workload, but with more dynamically created threads (n keys dispatched to a pool of threads/goroutines until the key space is exhausted) but I haven't finished the threaded version for comparison yet.