I've been looking into the fortress compressors also, because of the aluminum thanks and low noise ratings. I was interested in the 4 gal model at first, then when I heard about the 5 and 27 gal models that were coming out I decided to wait till they hit stores. I looked at all of them yesterday, and I was able to hear the 27, 4, and 2 gal models run. The 27 and 4 gal sounded about the same, and seemed to be louder than I was expecting. I have a Kobalt 20 gal compressor that is rated at 82 db, but the tone and volume of this compressor is making me want a quieter unit. I was disappointed when I heard the bigger Fortress compressors since they weren't much quieter than my Kobalt, and I was ready to pull the trigger on the 27 gal. After hearing the bigger ones, I plugged in the 2 gal fortress for the heck of it and it made me smile. The 2 gal is quiet, albeit it doesn't have the output of the bigger units the noise difference it's totally worth it. I ended up getting the 2 gal and it's going to be my go to compressor for small and simple tasks, and I'll keep my Kobalt for when I need more volume and output. I ah also pick up one of the aluminum 7 gal tanks from HF for some extra capacity for the 2 gal. Another thing I love about the 2 gal is that it fills up fast and recovers fast. Down the road I may consider getting the 27 gal fortress to replace my Kobalt even though the noise level is similar. The aluminum tank, higher psi, higher cfm, and the quicker fill/recover time have me still interested in it.
The short of this is that the Fortress compressor lineup is impressive, and whichever one you pick up you'll be happy with.