Was running more tests on the full MR page with a friend. Results:
1. Extremely squishy vs LeBonk. LeBonk had 50 AP at level 1, I had 96 MR as MF. Took 40 damage from her Q. Her autoattacks were doing 49... I killed her with no problem and more than half my HP bar intact.
2. Kassadin vs Morgana. Kinda useless. Morgana just ignored me and pushed to my tower. Not so good against her (though it was kinda obvious).
3. Warwick vs Kennen. Kennen had 30 AP. It was kind of an even fight. Could have gone either way. The interesting thing was that again, he just gave up using spells on me and just used his autoattacks instead.
4. I switched out mana regen yellows for the 13 armour. Vlad vs Kennen. Won with no problem since now the autoattacks and goddamn minion aggro were much less of a pain.
So after 4 tests, I decided to use MR red, blue, quints and armour yellow. In all the tests I used 21 9 0.
The only real definitive result I got was that it really does make LeBonk completely useless. If I was using someone who wasn't absolutely squishy like MF and perhaps Udyr... it really would have been no contest at all.
Other than that, it's interesting that it allows me to manhandle Kennen somewhat. Kennen is one of the strongest laners in the game, especially if you just limit it to AP. The thing is that Kennen has really high base AD as well, so it kinda skews the results of the MR test. I'm still not too sure what exactly would prompt me to take out this page other than to deal with LeBonk.