SR farming

I've gotten UR from level 10s before even from losing from them

@below: what kind of noob lose to lvl. 10 LD? lol

you can btw get sr and ur cards from all levels i just got dark necrofear after losing against level 10

Also from my experience lvl 40s are the only ones who drop UR jewels, so there's that.

In Elegant May and Mokuba I got a lot of sr cards from lvl 30 so its pretty hard, but I always farm lvl 40 if I can

Yes! Always go for the lvl 40 LDs

Yes & No:
Yes: The card pool of Lv40 LDs is more restricted (the crap from regular duelists is no longer in there), so in a duel with similar end score, the chance of a SR card dropping is just way higher with Lv40 LDs (no doubt about that).
No: The randomness of the loot drops may make you doubt. A lot of chests hold keys, coins, gems or Rare cards.
So if the difference really is 15 drops in Lv 30 Vs 8 in Lv 40, then the chance of you getting an SR drop can be just as high with 15 drops on Lv 30 as 8 drops on Lv 40 (especially since getting high scores on certain LDs can be REALLY tough).