as has been stated, if you lost that much boost from a leak then the car would 99% also have a very bad vac leak at idle, and it probably wouldn't hold idle. Ocassionaly leaks do form only under boost though, that won't be there under vaccuum.
I brought my car to a shop for an exhaust job, and the mechanic forgot to retighten the lower IC tube. Where the tube met the IC the bolts were literally on just finger tight. The car, believe it or not, held an idle, and ran fine for the most part. I was grannying the car, so i didn't notice a power loss. That was until one hill on my way to work that i could normally pull in 5th at 1900RPM, i had to downshift to 4th and then even 3rd. My boost gauge was not working at the time so i can't comment on boost loss, but considering the power loss I can only imagine that boost was extrememly low.