This gets very close to the 67/min you would expect from a yellow belt of iron (see helmod below). To get the maximum blue plant output of 90/min, you would need more than a yellow belt of iron. It should go up to 75 with a bit more iron (e.g. second yellow belt or red section for the gears), to get 90 you would have to add more circuit production as well (and possible add more inserters, haven't tested). However, 67/min is enough to saturate 20 (blue) blue science plants, which should probably be enough for a speedrun (and to at least get you up to stack inserters / beaconed setups if you really feel like going gung ho on the blue science).
I'm not a big fan of looping back the circuits like this, but otherwise you have to make a really complicated setup to get enough circuits and iron fed into the plants. I also tried setting something up with direct insertion of circuits (1 plant to yellow, 2 to blue, and 3 to purple), but that is just horribly complicated so in a speedrun it is certainly not worth it. With stack inserters or inserter bonus it should be much easier, but that's not worth researching, certainly not early.
Note that the red inserters grabbing circuits before the loop are needed because the single yellow belt lane doesn't have enough capacity for the circuits. Possibly you can do with less, since total circuit production at 469 is only just above yellow lane capacity of 400, but that would require a fully compressed belt. Of course you can also use the full yellow belt by side inserting some production of splitting/balancing it, but that seemed more complicated than just adding some red inserters.
(Also Note that there's enough room to place chests between the yellow, blue, and smart inserters so any unused capacity is stored there, which is presumably more useful than buffering the smart inserters; but I prefer to have the basic stuff I need in a separate central location so I don't have to run all over the map to collect goodies)
Production stats
Helmod plan
blueprint string
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