Here's a list of the longest hits in several categories. In
italics, I list the longest theoretically possible links, followed by the longest known so far, in
bold.
Absolute longest hit:
20015 km (to discover)
20009 km
Chincha Alta -
Siam Reap
20004 km
Córdoba (14012) -
Hamilton (3206)
18821 km

Christchurch (8053) -

Wingene (8750) Seda - Talking Head (237 days)
2018-06-17 07:08:44
Within the Euro Area (countries using the Euro = Eurozone):
17640 km
Base Dumont d'Urville (98414) -
Miquelon-Langlade (97500)
09620 km

Karttula (71570) -

Saint-Denis (97400) Ratskin - dingchavez (548 days)
2011-05-18 06:54:00
Within the Euro Area in Continental Europe:
04281 km
Nuorgam (99990) -
Tarifa (11380)
03851 km

Albufeira (8200) -

Nurmes (75500) Karhu IVA - viivi14 (136 days)
2010-12-09 17:26:54
Flying over Euro Area land only:
02838 km
Cabo de São Vicente (8670-390) -
Osadné (067 34) (over Andorra too)
02829 km
Vila do Bispo (8650-406) -
Osadné (067 34)
02548 km

Brezno (97701) -

Amadora (2720-268) JARDO™ - Titania_eu (1157 days)
2016-10-23 12:09:10
Outside the Euro Area:
12846 km

Buzău (120083) -

Bahía Blanca (8107)
2019-11-18 01:19:51 (flying over the Euro Area)
08423 km

Akashi (6730000) -

Lviv / Львів (7907)
2017-03-26 18:55:49 (not even flying over the Euro Area)
Dead straight vertical line within the Euro Area:
03793 km
Lachania / Λαχανιά (85109) -
Nuorgam (99990)
02747 km

Tuuri (63610) -

Voula / Βούλα (16673) kirasi - loup1771 (304 days)
2013-06-11 01:00:32
Dead straight horizontal line within the Euro Area:
05301 km
Eberau (7521) -
Miquelon-Langlade (97500)
01252 km

Brasschaat (2930) -

Lublin (20-093) E-verzamelaar - alederp (38 days)
2012-05-29 16:53:29
Other categories welcome! I'm thinking of "Within the same country — for each of the Euro Area countries" (within Germany already
here, within France it's the 17640 km line mentioned above), "Within places sharing the same main official language", etc.
NOTE: this is a WIP. I had broken links to most maps for theoretically possible, so I just deleted the links and started replacing them with the correct ones (only two so far, sorry).