I highly recommend the Satisfactory Tools' production planner, it makes it so much faster to figure out how much of what you need to achieve a particular result.
It's making going nuclear look actually reasonable, something I never managed to achieve in EA
I mostly use belt speeds based on need myself, I find just going for top speed belts introduces potential issues with things not feeding correctly and overflows triggering prematurely... Besides, I find it more pleasing to see a line of slow build items moving to their destination than one at a time rocketing at ludicrous speed across the factory
Though, if we could literally rocket propel items from one area to another, that would be a different story ...