- Great Barrows would be L21 minimum to L25 maximum (Sambrog is L25). From personal experience, Sambrog is sort of a pushover, so I don't think a well-coordinated L21+ group would have any trouble.
- Fornost would be (if Allakhazam's entry is correct) L38 minimum and L42 maximum. L38 would be a bear. 42 would definitely be doable. I five-manned it with four L38-42s and an un-pimped L50 minstrel without much difficulty.
No clue where the whole Garth Agarwen cluster falls now. I always hated that place, so never bothered learning it.
Personally, I think the ultimate goal should be Barad Guluran. If you can walk out of that place at-level and undying, you truly have some bragging rights.