Well, you can spread out the forges if it's an issue with lag or screamers... or even just not have them at your main base. Have a "forge" base 500-1000m away. Only go there to smelt stuff or forge stuff. Then you only deal with screamers when you go there and you only have lag while there. Just an option if you want more forge speed with vanilla.
As a note, the devs said screamers will not spawn again for 21 (IIRC) minutes after they spawn, at least in that same area. I haven't tested that to see if it's working that way, but I know I've had screamers appear at a mine and after I killed them, no more appeared for a long time even though I was mining iron, which generates a ton of heat (I don't crouch and I use an auger, so lots of heat), so it seems to be working that way. So that means you deal with it once every 20-30 minutes or so if you remain in the area. That isn't so bad, really.