I'm kind of a perfectionist, so I always studied pretty hard for my writtens (like really studied, not memorize the answers over the weekend studying). As a result, I always did well and was able to show up to the oral with a strong test score. It helped set the tone for the checkride, which is obviously beneficial.

But I really don't think it's going to affect the duration and intensity of the oral, as there are so many other factors at play. After just a couple of minutes, the examiner will be able to determine if you know your stuff or if you're just trying to skate through. If you are one of those guys that memorized the answers but are thin on knowledge, expect a long, brutal exam. On the other hand, I've found from my own experiences and that of my students that if one walks into an oral well prepared, you will likely have an enjoyable experience. Examiners LOVE well prepared candidates, and will spend most of the oral relaying educational war stories and other tidbits of knowledge learned through their many years of experience. Plus, if you blow the examiner away on the oral, they will WANT to pass you. So if you screw something up on the practical test (which we all do, trust me), they'll probably give you a second chance.

Besides, I'm assuming you're going into this since you like it. Why wouldn't you want to study? When I was working on my ratings, I was reading about aviation 24/7 and asking all kinds of questions. If you're really interested in aviation and cracking the books, the knowledge tests are going to be easy.