It might be okay, my experience leads me to suggest against it but as I said you could risk it especially since your own experiences have been different. So, the goldfish are currently kept in 80 degree temps? If so, you can try it but, if possible, increase oxygenation as the new fish will of course decrease what's available for the goldfish. You again have to err on the side of caution as Gourami's don't like a lot of current, but surface agitation is the best means AFAIK of increasing gas exchange and dissolved oxygen levels. And of course, monitor the parameters due to the increased bioload. I also don't know if the Goldfish will find the Gourami's pelvic fins specifically tempting.