If you've been testing the final Windows 7 Release Candidate on your own physical platforms, and you wonder what's giving you that feeling that it's just a bit peppier, a tad zippier, it's not an illusion. Betanews tests all this week, concluding today, comparing all the major stable release and development Windows-based Web browsers, running on exactly the same physical computer with fresh Windows Vista SP2 and Windows 7 RC partitions, confirmed what our eyes and gut feelings were telling us: On average, most browsers ran 11.9% faster in Windows 7 than on the same machine running Vista SP2, with most speed gains falling right around that mark.

Internet Explorer 8, for example, runs 15% faster in Windows 7 than in Vista SP2, in multiple tests whose results were within one another by a hundredth of a point. Using our performance index as a guide, if you consider the relatively slow Internet Explorer 7 in Vista SP2 as a 1.00, then in a fresh test of IE8 on the same platform, the newer browser in Vista SP2 scored a 2.03 -- performing generally better than double its predecessor. But in Windows 7, the score for IE8 rises to a 2.27.

In indications that Mozilla's developers may be testing their development builds on Windows 7, both of Firefox's private development channels show greater performance boosts from Win7 than for the current stable release and the current public beta. Firefox 3.0.10 enjoyed a nice shot in the arm with a 116% speed gain over Vista SP2, and an index score of 4.36 in Win7 versus 3.96 in Vista. Firefox 3.5 Beta 4 saw a speed gain at right about the average, 12%, with a Win7 score of 9.29 versus 8.49.

But in tests we repeated just to make certain of the results -- again, with very minimal deviations, and some dead-on exact time values in the SunSpider when repeated -- yesterday's daily private developer build of Firefox 3.5 (once slated to be called "Beta 5," but which may be promoted) posted 28% better speed in Win7 than Vista, and the 3.6 Alpha 1 "Shiretoko" build was 30% faster in Win7. The 3.5 probable-RC scored a 9.20 in Win7 versus 7.62 in Vista; and 3.6 Alpha 1 scored a 9.10 versus 7.45.

Today, we began testing the new Chrome 3 browser, Google's latest development channel build, as Chrome 2 proceeds to the "Stable" column and Chrome 1 is put out to pasture. We noted that Chrome 3 currently scores a 94% on the Acid3 test -- a setback from Chrome 2's 100% score which we can only assume has to do with something the Google developers are in the midst of testing. That slip up almost completely wiped out Chrome 3's faster rendering and cryptography benchmark index gains, with build 3.0.182.2 scoring a 12.24 in Vista SP2 against build 2.0.177.1's score of 12.23. But in Windows 7, Chrome 3 shows more improvement, indicating that even Google is taking apart Microsoft's new operating system in the labs. Chrome 3 was faster in Win7 by 16% compared to Chrome 2's 12%, and Chrome 3's index score in Win7 was 13.86 and for Chrome 2, 13.43.

Opera's raw performance in our tests thus far continues to be unremarkable. The stable release version 9.64 benefits almost not at all from Windows 7 -- just 2% -- with an index score of 4.55 in Vista versus 4.51 in Win7. But the public Opera 10 Alpha build fared much better, gaining 15% more speed in Win7, and scoring a 5.47 there versus 5.03. The latest Opera snapshot build, which now includes the "Beta" graphics and a new look-and-feel, saw an 8% boost from Win7.

The absolute shock of the day, however, comes from Apple. For reasons we can only surmise Apple's developers must be studying (if not, they should be), the latest Safari 4 Beta build 528.17 runs 22% slower in Windows 7 than in Vista SP2. In fact, Safari 4's index score slipped behind those of both Google Chrome 2 and 3. We reconditioned our test platforms twice just to verify, and once again, the variation was minimal and the results were confirmed: Safari 4 scored an 11.43 in Windows 7, versus that staggering 14.12 in Vista SP2. This while the stable Safari 3.2.3 enjoyed an 18% speed increase in Windows 7.

Unexplained anomalies notwithstanding, the evidence is mounting that all browser developers will be receiving a gift from Microsoft, probably by the fall, in the form of 10% to 15% better performance without having to lift a finger.