I've got the heavy plasma and the assault plasma, and am currently researching them.
If I understand Kordanor's tech tree right, though, you don't have to have researched plasma weaponry to get to Mag- you just need to pick up the other two alien guns. how soon do they appear? can lasers bridge the gap?
the reason I ask is that it seems to take an exceedingly long time to manufacture a squad's-worth of kit, not to mention grinding crashed ufos for raw materials, and I'm not really looking forward to making a whole bunch of plasma rifles when I could be building Corsairs instead