The Omega ride goes out from the back of Omega cycles at 0600 on Sat morning. There is often a fair no. of people - 30-40 last time I was there, with a broad level of skill in bunch riding. Includes a lot of triathletes (I think) - read into that what you will. Friendly bunch, do approx 70 to 100km, depending on the loop. Ian will email you out the course for the week if you sign up on the Omega cycles website.
Regarding the TWI ride - probably a good one to do if you are racing Sat arvo!