The Penn Station main waiting room was the largest for three years, until GCT opened.
The above ground building of Penn Station was larger than GCT (about 1.5 acres I think), and it had a 225 foot arcade that led from 7th Ave to the waiting room. But the main room was slightly smaller, although higher.
PS........277 x 103 x 150
GCT......287 x 120 x 125