And thanks for the replies, though I'm interested in specifics, as in who here, who weighs around that much and drinks whiskey can tell me from experience, in cups not bottles.
Well, first of all, you don't measure whiskey in "cups." Secondly, as a novelist, you can set whatever limit you want, as long as you adequately explain it to the reader. For instance:
"Oscar sat at the bar, looking hazily at the bottom of his glass of whiskey. Two empty glasses sat nearby, reminding him of how he arrived at this point in the evening. Although he was an experienced drinker, he never seemed able to get beyond the third glass. 'You're a lightweight!' his fraternity brothers would kid him, but as his mind drifted to thoughts of Ramona, he knew they were right."
As opposed to this:
"Was it his eighth or ninth. Oscar couldn't remember as he slammed the glass down on the bar and called to the bartender: 'Gimme another!' The bartender eyed him with a mixture of suspicion and pity. 'Don't you think you should call it a day, mister?' 'Listen here, sonny,' Oscar sneered, 'I was drinking a fifth of bourbon every day when you were still sucking at your mother's teat. Now gimme another!'"