Let's take the two consensus greatest point guards of the modern era, Magic Johnson and Isiah Thomas. Paul gets the Thomas comp often, but most would list Magic atop any modern era list. Fair enough: those two were great, great players, a pair of the best players in our league's history. And Paul -- at age 22 -- is already on par with them.
The following graph displays some figures for the best statistical season for Paul, Johnson and Thomas. For Paul, of course, it's '07-08. For Johnson, we went with 1986-87. For Thomas, it's 1984-85. We took per-game box score statistics and made one crucial adjustment: pace. (This is something suggested by the great Kelly Dwyer.) We adjusted each player's figures to suggest what the player would be done if his team played at the pace of 100 possessions per game. If we don't make this adjustment, a player from a slow team has a material disadvantage in racking up numbers: if Player A's team has the ball for 90 possessions, and Player B's team has 105 possessions, then there are more opportunities for Player B to get a point, an assist, a steal. Adjusting for pace just evens this out.
So let's take a look at the pace-adjusted numbers.
Remember, we aren't using PER, so there's no killer, one-number statistic to point at. This is just your basic point guard rundown: points (Paul and Magic land within a tenth of a point of each other, Isiah was not as potent), assists (Isiah has a small advantage over Paul, and a substantial lead over Magic), rebounds (Magic leads the way, thanks to his large frame and enormous hands), steals (simply no contest, as Paul tallies 50% more steals than Isiah and nearly twice as many as Magic) and turnovers (Paul coughs up the ball far less frequently).
Judging by this, you'd conclude Isiah's peak doesn't quite match up with those of Paul and Magic, yes? Thomas scored really well for a point guard, but Paul and Johnson are on another level, some 16% higher. The lead over Paul in assists (about 2%) in nominal, and nothing else Thomas does exceeds Paul's performance.
What about Magic and Paul ... whose statistical peak was better? The race for points is dead even. Paul averaged roughly an additional assist per game (pace-adjusted). The rebounding edge definitely favors Magic ... but Paul saves a full possession with regard to turnovers and earns almost twice as many steals. What matters more from a point guard: two extra rebounds, or an assist, 1.3 steals and 0.9 turnovers? I certainly feel comfortable giving the victory to Paul.