An eternity in four seconds

Mission accomplished, clearly. Not only that, but exceeded: the improvement was already more than six seconds, rather than five. But numbers alone don't tell the full story of what is happening in Formula 1^® right now.
Raikkonen's fastest time of the Barcelona test could have been even quicker. Looking at the pattern of laps and visits to the garage it was clear that the top cars were still holding something back. Adding up the best three sector times from the final test day resulted in a theoretical fastest lap of 1m18.3s. In which case, the gain over the 2015 pole would increase to about 6.3s. 
But by the time the European season traditionally begins with the Spanish Grand Prix in May (as will be the case again this year, with the race weekend scheduled for 12-14 May) track conditions will be faster than those found in pre-season testing. Despite the sun shining throughout most of the two weeks of Barcelona testing, track temperatures struggled to climb past 30 degrees centigrade. By May (assuming it doesn't rain) those track temperatures could exceed 50 degrees.
Full summer conditions, in other words: the ideal setting for the tyres to do their work. So we shouldn't be surprised if pole position for the Spanish Grand Prix manages to creep down into the low 1m18s or high 1m17s. That would put the improvement compared to 2015 lap time at more than six and a half seconds. And more than four seconds faster than last year's pole of a neat 1m22.000s
So here's the point: what do such improvements from year to year really mean for Formula 1^®? Essentially, they mean an eternity.
From the start of the hybrid turbo era in 2014 to now, the time improvement in fastest laps at Barcelona (set during the race) has been just under two seconds. In the three races between 2004 and 2006 (before the installation of the chicane prior to the pit straight) the evolution in fastest lap times added up to just 0.8s in total. And those were the fastest F1^® cars of all time back then, with 2.4-litre normally aspirated engines and an overall weight 120 kilograms lighter than it is now (without the driver). Just those extra 120 kilograms on their own would be enough to guarantee lap times five seconds slower… 
In 2013, the final season of the normally-aspirated era, still with cars that were much lighter than today, pole position for the Spanish Grand Prix (set again by Rosberg and Mercedes) was 1m20.7s. In other words, more than two seconds slower than Raikkonen's fastest time at last week's test.
And now it's best to stop there, before getting mired down in numbers that require increasingly detailed analysis and context. Let's cast an eye to the future instead. These ultra-rapid 2017 cars are the result of more relaxed aerodynamic rules (allowing around 25% more downforce) and Pirelli tyres that are about 25% wider than before. The result is cornering speeds that are considerably faster – up to 30kph more out of the exit from the famous Turn 3 in Barcelona: the fearsome uphill right hander that follows on from the right-left corner at the end of the pit straight. But we're only just at the beginning of a new era. These tests in February and March demonstrated that the cars were remarkably reliable (with a few unfortunate exceptions). It's clear that turbo hybrid technology has been mastered by teams and engine suppliers. So it would be logical to expect an improvement of around two seconds over the course of the season, as opposed to the second and a half that usually forms the margin of progress during a single season. Lap records being broken left, right and centre will underline what we've been saying for months: this will be the fastest era of Formula 1^® ever seen.