Brendan Moran's excellent Dublin - Cork route
http://members.uktrainsim.com/filelib-info.php?form_fileid=25225 (UKTS file no.25225) might fit the criteria.
90+ miles : Yes. 166 miles long, with 85 miles scenicked (spelling?) and the remainder a w.i.p.
Not Resource intense : I would class it as in the middle resource intensive wise. On my middling computer it runs decent enough, WCML is the only route i have trouble with.
Doesn't require alot of payware : No, IOW route and the class 66 loco, which maybe you have already.
Any Country : Ireland.
Not a Mountain Route : No.
It does require a good few freeware files, but if you decide to download the route, PM me and i might be able to help. Also as i don't have Armstrong powerhouse lighting enhancements i don't how it would interact with this route.
Just a suggestion it might be worth a look at and see what you think.