There is no limit, but anything you over commit will be paged and remember that a swap file needs to be created which is equal to the amount of RAM assigned, so you give it 1TB its going to have a swap file of 1TB.
in my environment I run between 200 - 300% over commit with zero performance impact, when running in a large environment that has a standard SOE the amount shared with TPS is insane and ballooning takes care of the rest.