I don't have a straight side-by-side comparison between Lomo CN 800 (or Max 800) and Portra but I always got good scans and prints from this film.
(both printed on Fuji Maxima paper)
Color rendering is what I would expect from a modern Kodak pro film and under maximum enlargement that I can achieve in my enlarger I don't see a difference in grain (unsurprisingly since even Kodak rates them the same (as well as in any other technical parameter - compare
Portra 800 and
Ultramax 800 spec sheets)).
I noticed now that you are talking about 120 film (which might be different to the film format discussed here). I only use this film in 135 format, but for me, it's the perfect substitute for Portra 800. I only buy Portra 800 for travels, because it comes in a single box and I can save the TSA personnel the trouble of taking the cassette out of the canister to swipe it individually which they will do if they see film without original box.
Lomo CN 100 and 400 are a different matter. Clearly based on older emulsions (personally never liked them much).