I have never been to Plainfield, so my apologies if I am incorrect, but:
I checked out Google Earth while watching the telecast and seeing the shots into 18, and being surprised by some of the commentary. I usually find that CBS - McCord in particular - inflates the distance that the pros are hitting the ball. They seem to "forget," or not notice, situations where the tees have been moved forward (For example - the 18th tee at Atlanta AC for the last round of the PGA).
According to Google Earth from the forward tee on Plainfield 18, (the one that I believe the pros were playing) the carry is 253 from the back of that tee to the front edge. From the tee closer to the 17th green, the carry is in the 295 range.
On the 9th hole, the carry is approximatley 305 to reach the fairway above the second bunker from the right - from the tips.
I understand that both carries are significantly uphill, and perhaps I am looking at the wrong information, but I can accept the idea that Steve Stricker, Jim Furyk etal can perhaps carry their driver 250 + yards uphill and that Dustin Johnson could carry his 3-wood approximatley 260 yards to the middle of the green. Although I wish those distances could not be achieved, I can accept that those seem "reasonable" given current technology.
If Stricker/Furyk are carrying their driver 300 yards - and DJ his 3-wood - as CBS would have it, then we are in great trouble indeed.
My technological shortcomings prevent me from figuring out how to upload the Google Earth image with the distances laid out. Perhaps someone else could do that to better answer resolve this question.