I don’t understand how it thinks this is better dps to lose sp and crit for 6 int… feel like a bug.
To better answer your question, we would need to see all of your settings. Press the “help” link next to the big Best in Bags or Best in Slot section header, then follow the instructions to create a snapshot. Post the ID in a reply to this thread, then we can take a closer look at your case.
You are optimizing for a 90 second fight, where mana will be a limiting factor. The mp5 and extra intellect will ultimately edge out the extra spell power/crit. Fight length affects optimization significantly in classic because the margins are so small between different gear setups.