Yeah, I was going to say, you can rent either mitre/compound mitre or regular chop saw. Chop saw is made just for this, cutting strut (steel). I have not tried to do it with a sawzall, but I got to think you would get a more square, cleaner cut with a chop saw where the piece is held in place and you're hitting it at a direct 90° angle. Then again, you said you tried that and went back to the sawzall. I just can't get that in my mind how it would be better. Maybe quicker, but not more accurate, can't be. I have used sawzall a bunch of times, but never on steel, so I can't attest from personal experience. But I think a large chop saw (>12" blade) would have to do a nice job.