Rick - I believe that it varies depending on the cam and the cam timing. On my set up below when I had the E cam, my closest clearances occurred at TDC on the exhaust valve, and at 5 ATDC on the intake. In any event, 5.0GT nailed it -- if you make a 'map' of the clearances from about 30 degrees on either side of tdc (during overlap) in 5 degree increments, you'll see where the closest point is.
SS - you do need to measure no matter what someone else's combo did if you want to be certain. Best thing you can do is work with a reputable vendor that will take a cam back (that hasn't been run) and allow you to buy a different one - assuming you cut it too close, and you don't want to cut the pistons. When it looked like my original E cam was gonna be too close, Central Coast Mustang actually sent me out a milder Crane grind - and allowed me to send back the one that I ended up not using. All I paid was the shipping -- pretty good customer service I thought.
Ultimately I ended up with a custom - I'm with Gearbanger; focus on getting the right cam for what you're trying to accomplish - not the 'biggest'.