The way I have been measuring the *performance* of the systems is the number of documents per hour that our system can process. A "document" is an image with a lot of business data surrounding it. My peformance needs are to process 15,000 documents per hour through a 'workflow' engine. We are close to that. The query time has always been sub-second, wether READ UNCOMMITTED is user or not, however, the system throughput slows down 20-30 percent when READ UNCOMMITTED is on. So instead of 15,000 per hour I go down to say 11,500 documents per hour.
Our application and database runs fine under low loads, it's when the everything gets cranking up that we notice the hit on READ UNCOMITTED. Always trade offs. Locking contention verse speed.
If I learn more I'll be sure to post it here.