I thought Id drop you a line after spotting your thred in the forums,great idea including distance in the tittle.
Ive not long started on a long track of my own so Ive posted my link here incase your interested in checking it out.
There was another bloke (who's now retired from track building) by the name of DMz who was building long distance point to point tracks like yours,
the longest of which (from memory) was 50km or 30mile & called Mt Arrowsmith, there were a few others he did; Col de Turini & Race to the Sky would probably be of interest to you as well if just to check out how he went about it.
If you dont already have them try the temporary circuits on the rFactor central site.
As for feasable, it should be, although it depends on the PC your using in regards of track length from what Im given to understand.
With Mt Arrowsmith for instance, he also provided HAT files to take the pain out of first time loadings, as a lot of people had troubles with it.
Also DMz himself had troubles loading due to PC spec' & had to limit the track length by about 10km's.
Dont let this put you off from trying though!
Someone else WAS working on the I.O.M.TT course but it was the building textures combined with distance that did it for him (Booo!),this was some time ago & PC's are improving constantly,what doesnt work today could be the norm next year!
The other issue could be elevation giving the skydome grief as can be seen in Race to the Sky, although I believe he did work
out a "work around" for Col de Turini.
Lastly, some of these tracks may not be the prettiest to look at, but he was after quantity not quality & a quick production time.
Being a noob myself I can only go by the researching Ive done for my own track & suggest that you just give it a go-the old engineering
principle of "suck it & see" approach- as there's so few people working on these long tracks to hit for advice.
I must say it's good to find someone else who's doing something similar & I look forward to hearing from you & seeing how you go with it.
Best of luck,
Make sure you use the surface tool to 'slice' your track in parts. It will create a seperate GMT file for every surface (or slice) created.
That way, you can set individual LOD distances for each piece and hopefully help towards keeping a decent FPS.
This is something thats not worth doing on regular tracks, but should be useful on these monster tracks you fellas are doing.
EDIT: Just thought of something else.
Be selective about what you allow to be viewed in the mirrors. By default, i think BTB selects everything to show in them, but maybe just do a small ratio of track side objects.