Performance - R9 290X @ 1080p
Our very first benchmark - Unigine Heaven 4.0 running at 1080p - already shows that in some instances the performance of the Radeon R9 290X decreases after the initial benchmark run. The liquid cooled setup and Uber profiles did not show any variation, but both of the Quiet profile setups show a very noticeable performance drop after the very first benchmark run.
Although the Quiet profile does perform slower than the Uber profile, if you look at the fan speed logs you can see the benefit of using the Quiet profile. With the chassis fans at 5v, the Quiet profile keeps the fan running about 20% slower than the Uber profile, which is a very large and audibly noticeable difference. One other thing to point out is that with the exception of the liquid cooled setup, each configuration runs pretty much constantly at 94 °C. So if you are planning on purchasing a R9 290X, don't have a heart attack when you find that you can almost boil water on your video card while gaming.
Metro: Last Light gives us very similar results to Unigine Heaven, although we actually see a very slight performance drop after the first run even with the Uber profile and Liquid cooled setups. It's not much (between .43FPS and .69FPS), but the fact that it happens on every single configuration indicates that there is a very small performance drop even in the best cooling scenarios.
The Quiet profile again shows a performance loss over time, but the difference is much larger than what we saw with Unigine Heaven.
Analysis - R9 290X @ 1080p
As expected from the graphs in the previous section, the Uber profile and liquid cooled configurations don't show much of a performance drop in either Unigine Heaven or Metro: Last Light at 1080p. This means that for a single R9 290X using the Uber profile, online benchmarks should pretty much always be accurate - at least at 1080p.
The Quiet profiles, on the other hand, showed a performance drop of about 5.5% with the chassis fans at 5v. In other words, when using the Quiet profile there is the possibility that online benchmarks may be off by as much as 5.5% at 1080p if the reviewer did not perform multiple benchmark runs, discarding the first four or so benchmark runs.
This brings up the question of how much of the maximum performance possible you should you actually expect when using the Quiet or Uber profiles in various cooling setups. The good news is that with the Uber profile, you are likely to see pretty much full performance regardless of your cooling setup (within reason of course).
However, if you use the Quiet profile even in a very high airflow chassis with the fans running at 12v - which is actually louder than the Uber profile with the chassis fans at 5v - you should only expect about 95.3-97.6% of the maximum possible performance of the R9 290X. If you want to use the Quiet profile in a quieter chassis with the fans at a much more reasonable 5v, you should expect to only see about 93.2-93.7% of the maximum performance. This is a significant performance loss, but is actually not bad considering that the GPU fan runs about 20% slower when in Quiet mode.