Thanks everyone for the replies. Some interesting and informative stuff in there. I think I get the point :-)
Just to answer/respond to a few things :
#Guitarhacker - yeah, my "room" is a mess, acoustically. Well, its not even a room really, its more like a cupboard. I have acoustic panels in it, and leave the door at the back open (as someone else on here suggested). Still, I do spend more time listening on (top quality) headphones, than I do listening through monitors (Yamaha HS80, one with a dodgy hissing radio frequency .... I'm thinking my "cupboard" is probably too small for ARC.
#dmbaer - I export at 44100/24 bit. I think the exported unmastered wav sounds OK, but when using Ozone, particularly the limiting, I can hear it can affect the sound not in a good way. But, even when it sounds reasonable in Ozone, it can sound awful somewhere else.
#Jeff Evans - thanks for some great suggestions and advice. just one thing : I am comparing my tracks mainly not to professional music, but tracks on Soundcloud that are similar-ish. So, mastered tracks yes, but usually, at least attainable. I find its my bass which sounds most "out" in comparison.
#Kalle - I don't actually A/B from inside the project, thanks for the tip. I do compare outside the project using ozone to check the overall frequency of other songs.
#bitflipper - ha ha, I had even though the same! Kalle, missä sä asut?!
#AT - I think mostly my mixes in Sonar are quite low - eg, peaking at something like -12db, or maybe more. Is it better to up the levels to get it up naturally to more like -6/-3db, meaning less limiting? I notice when limited a lot in Ozone - this is when I can really here something bad coming in, not quite distortion, but pushing it certainly degrades the overall sound. I'm not sure what is considered "a lot" though ... pulling the threshold down to -9/-10, maybe that's too much, or maybe it depends on the source material?
Anyhow, I'm in a rubbish room, with electrical issues, how much worse can it get :-) I'll probably go back to basics, keep things as simple as possible, and try and learn where it starts to go wrong.