Well, looks like I found the breaking point . . .
2 lances of bugs with PXH lance leaders
lance of heavy tanks
lance of vedettes
lance of upgraded vedettes
lance of heavy hovertanks
artillery tube
company of infantry
Rebels lost 3 mechs . . . Stinger took a LB-10X slug through the rear torso, FS9 got its head blown off, and a Battle Hawk took a beating to fall down. My own lance got shot up . . . the Thug took several weapon TACs and lost a shoulder while armor was falling off and unable to hit with PPCs. Grasshopper 6K and Penetrator 4D both got knocked down while my Victor started taking internal damage, including the loss of a gauss slug bin. Lots of armor damage with the assaults starting to take internal damage.
Tyrant's forces lost 2 Wasps and a Stinger, had a Stinger legged, heavy tank, LBX vedette, hovertank skidded off a cliff. PXH and FS9s shot up but mobile. Pillboxes got shot up, but not to collapse.
Not sure I came off the better . . . but with AA defenses weakened, time to call in the air strikes. The ground forces are also going to lay seige to the firebase and start raining some artillery on the site.