If budget is not a constraint, then I'd highly recommend the buffet at Conrad. It is expensive but worth it.
I'd add Senses (Mariott Suites) to the list - they have a great, reasonably priced buffet. Both this side of town (KP side).
On the Aundh / Baner side, JW has good food. I have been to Shakahari which has good fare (vegetarian only).
We used to take our team of 20-25 people to a bunch of places at Viman Nagar. But if budget is not a constraint, I'd recommend these options.
Conrad and JW would be about 3K per head - but I am sure you can negotiate a better rate. Esp on week days. Senses will be around 1500 per head.
If you want a more casual experience (reasonably priced?) but with decent food, Barbeque Nation is not bad as well.