With turrets and everything I think it's about 45K tris. I ran it on Ella Deep Strike one, the final battle has 1 Orca (45K) 2 new Barracudas (3,800 each), 3 shrikes (16K each), 3 tbolts (21K), 3 excals (17K), 3 panthers (6.5K), 3 mantas (5K), 6 Morays (3K), and 2 tritons, those are the originals. and no noticeable frame rate issues. I'll try again with the FPS counter on, but it ran smoothly at or near 65 FPS the whole mission.
It ran at 65 FPS the entire mission except for about ten seconds or so at the start of the final battle where it dropped to 63 FPS then jumped back up.