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When I called Marineland in Dec and asked the question, I was told only the bottom was tempered. I would give customer service a call to make sure that hasn't changed. Marineland 75g only comes in brown trim which I didn't want. Aqueon 75 and 90g tanks bottom and sides are tempered.
You should do the test before drilling regardless. I was at a LFS recently and was going to pick up a Marineland cube. I asked about being tempered, and they wouldn't answer. They recommended buying a reef ready one (I want it done my way so I didn't). They had a few customers whos tanks shattered when drilling. They stated that Marineland uses tempered on the bottom only, but will use tempered for any pane if they didn't have enough non tempered for the tank.