Short update on the "interrupted download for big files" (see my post above):
After successfully downloading 5x500 Mb files in a raw I can now safely confirm that JD2 beta indeed fixes the issue!
I'd also like to add that this is actually a FEATURE provided by the beta, not a bug fix: as I reported in my initial post, the problem doesn't come from the stable JD plugin anyway, as downloading big Uploaded.to files in any browser will raise the same issue! So this definitely seems like a /default behaviour/ from the host (hence my suspecting that it was possibly done on purpose...?). Yet JD2b manages to work around this problem somehow.
Truly a great tool.
So support worthy free software people!

And my many thanks to all at JDownloader staff for their amazing work.
Cheers!
-- Angar