I've spent the last couple of evenings in the Late War arena. My frame rates are fine, but I've noticed some lag. I had a P51 salivating over my 1-engine 262, and "helped" him die by flying him to where it was easier for a friendly to get into firing position. At D600 behind me, I heard the friendly shoot and the Pony disappeared a second later; no smoke, no explosion, no parts...just disappeared.
Maybe this little bit of lag is common in LW...I haven't spent much time in there. I'll keep watching to see if anything changes over the next few sessions.