to be honest with you at that low of a point game I would go with 2 guardian squads with scatter lasers. This will allow you to sit back and punch marines from cover with strength 6 shots. Might go with EML on the walkers to krak the marines. Of course guide would work there. Anyway the scatterlasers will cover the banshees as they run forward toward the enemy. Also look at Harlies vs banshees.