You can get the upgrade for $84 (4 to 5 to 6) if you you go through audiodeluxe - ask for a quote - which they email you. It's 50% and then their own discount. Figures may or may not vary.

It will cost 399.00 for me to upgrade from my Ozone 5 to Ozone 6 advanced....unless one of you guys knows of a sweeter deal. This is the deal I'm getting from the Izotope website. I'm on the fence. 
 
Ozone 5 and I'm sure Ozone 6 use several excitation and expansion modules , basically adding in harmonics to get the same or a similar effect that you get with analog equipment. It's the way they have laid all of it out that makes it efficient and a better way to work IMO. T-Racks has some really good modules in it too and is equally effective in my opinion.And the modules in Ozone 5 are good. The multi- band compressor is great. I don't use the reverb as much. I think it's better to put the reverb on a reverb buss. I'm not sold on buying it for the EQ entirely....although I'm sure it's a great EQ. One neat feature is that with O6 you can drag and drop module order...something you needed to do with keystrokes an mouse before....but as Bit says....a lot of the change is eye candy over O4 and O5.
 
I'm interested in the metering. When O5 advanced came out I was on the fence then too and in the end I couldn't justify spending that much for metering, but good and accurate metering it is. I'm asking myself how much better I can work with the extended metering in O6 . Most of us have some form of accurate metering already and the two things at either side of our heads should be what we mainly rely on right? I'm not sure how much of an advantage it would be. Can anyone comment on O5 Advanced and are there other tools that are better or just as good? Each channel in Sonar X-3 has an EQ with metering in the background. I have SPAN and it's pretty darned accurate and fast.I have some really good level meters besides the one in Sonar. I don't get a 3d representation of my master channel...do I need it? If it really helps in a mix to see colored graphs and 3d art then maybe I'll fall off the fence toward Ozone 6 advanced. Can I spend 399.00 somewhere else and get a lot more?

T-racks seems to be underated here for some reason. I like to export mixes and use the standalone version to master while at the same time using a Sonar project and all of my 3rd party tools to master. It's always an interesting exercise.

T-Racks is definitely a viable alternative (and currently on sale for 80 bucks). So is the FabFilter Mastering Bundle. Elephant is another inexpensive alternative, at least for the limiter section. Meldaproduction has mastering goodies not found in any other bundle.
 
Truth is, if you have the necessary knowledge, experience, and patience you can accomplish everything Ozone has to offer using only free and inexpensive tools, or just SONAR's built-in tools. There is nothing that makes Ozone a "must have".
 
However, what makes Ozone stand out from the crowd is how easy and quick it is to get good results even if you don't know what you're doing. It remains my first recommendation for beginners. But even for old hands at mastering, it can't be beat for convenience and speed. If I'm mastering my own stuff I'll open the toolbox and see what works best, but if I'm doing a quick 'n dirty demo for someone else, it'll always be Ozone by default.
 

I love T-racks. Some of the best mixes I've heard over on the songs forum went through T-racks plug-ins in the master.