The cuts with lots of slag, look like you're going too slow, with the result you're getting a wide cut, with possibly a lack of air flow to blow the molten metal away.
Stupid question, but is the base of your table open? Some of the cuts almost look like you're trying to cut over a sealed base, with the result the air is blowing back up.
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The 10mm cut looks good. I'll admit I'm a bit dubious about the quoted specs, as I've got a 60A cutter that is rated at 12mm, and that is it's limit. It will cut 1/2", however it's definetly not a clean cut, with there being a noticeable trailing edge at the bottom of the cut.