Crossing the Universe[]
Hal Jordan and Guy Gardner are capable of flying to the edge of the universe in just 10 hours, while their rings are on standby mode. I.E, this is far from their greatest flight capacity.
Feat was already calculated:
https://forums.hero-academia.com/xfa-blog-entry/green-lantern-cruising-speed.17641/
The resulting speed was 40,734,000,000,000c
Kyle Rayner's MFTL+ Car[]
In this feat, Green Lantern Kyle Rayner crosses over 10 Lightyears in a very short timeframe by driving a construct Car. As this was done with immense casualness, and as it was a vehicle he'd need to manually drive it (And indeed, you can see that he does fancy spins and such with the energy trail), this would naturally scale to his Reaction Speed as well as flight.
This feat was already calculated:
Low-End: 10 minutes: 94610000000000/600= 525,974.98411051c
Mid-End: 5 Minutes: 94610000000000/300= 1,051,949.9682244c
High-End: 1 Minute: 94610000000000/60= 5,259,749.7299282c