I've got exactly the same problem caused me a lot of headache at the moment. I usually save the NRG file to my harddrive before burining it into my DVD. With NV3 it is working well and very reliable. However, after I have changed to use the NV4, I never been able to control the file size anymore. Sometimes it come up with 5.1 GB sometimes larger than 6 GB.
I was trying to reduce the quality of the project as well, but the result come up the same. I have tried so many times almost a week already, and it is a kind of waste of my time because doing one project take me 4-6 hours.
I don't think using Nero Recode is a good idea. You need to take hours to finish this apart from the first step.