ME here with my PE. Worked on both small capital and large retrofit projects in the field only, no true "design" engineering. Learned more "practical" knowledge in the field, but the book knowledge was still pertinent. You just had to know when to let that book go and look at what was in front of you in the field. For design engineers, I must say its much harder trying to design something for a retrofit rather than a green-field. Tolerances add up and all of a sudden that pipe that looked good in the 3-D modeling program runs right through a W20 beam in the field. Then you have to go back to specifications to see how you can adjust the pipe to fit with the requirements.
As far as the PE is concerned, it was pretty brutal, but if you have a good study schedule in the months leading up to it and tab your reference manuals, you should be OK. I took a backpack with 4-5 books while the guy in front of me had a full sized suitcase full of, I think, every book he had. I almost had a panic attack at the end of the morning session, but had 30 mins to spare for the afternoon session and was able to get out early. Promptly went straight home and guzzled 3 beers to relax and calm down. Waited a few weeks and got the pass letter. Much relief.