It says "lower spec"

Technically a preemptive kernel will be slower then a non-preemptive one in most complex benchmarks. This is because going from process to process rapidly means more context changes and thus you lose out on cpu memory cache and all that.

But since the desktop is idle 99% of the time then it's easy to make the justification that it's worth it to say "Ya it takes a couple milliseconds longer to open a webpage, but this way I can do it without getting my music interrupted or keep my game/movie framerate high."

Intel developed a tool called latencytop that can be used to identify processes that are hogging the system and can causing usability or deterministic time problems.

Remember the point to having 'realtime' performance is not to make things _faster_ per say.. it's to make things more deterministic. So you know how long it will take to get something done. On a very hard-ish realtime system you can say "It's going to take a maximum of 30msec to accomplish X task" and you can depend on it. On a typical Linux server system it may take 5-10msec most of the time to do the same amount of work, but if something else is going on then it may take 500msec or more; You can't tell how long something is going to take, even though it's likely to get done faster on average.

This sort of trade off is what you need to keep your video smooth, games fast, music interrupt free, scientific measurements accurate, robotic assembly machines from zapping the wrong parts of a chassis, etc etc. Anytime you need to interact with the real world....

So ya.. benchmarks are very difficult and are skirting the issue.