If we're listing luck-based courses, I believe these are 7's:
Toad Circuit
Cheep Cheep Beach
Daisy Hills
SNES Rainbow Road
Luigi Raceway
Maka Wuhu
Maka Wuhu was dumb pre-patch because of the glitch and post-patch because the gliding section was a load of bullshit.
As for 8 I'd go with:
Mario Circuit
Mario Kart Stadium
Excite Bike
SNES Rainbow Road
Dry Dry Desert
Yoshi Circuit*
Rainbow Road 64
Toad Turnpike
Water Park
Sweet Sweet Canyon
Thwomp Ruins*
Donut Plains 3
Toad Harbor
Moo Moo Meadows
*Technical courses that manage to be deathtraps anyways. It's very impressive course design. Ice Ice Outpost should probably also be here but that would be admitting that it's a deathtrap so I'm not going to put it there. <3
...Okay, I have to be remembering things wrong because I don't want to admit that 8 has *that many* luck-based courses, especially in comparison to the other games in the series. >_>