7 or 6 gears: starting or racing?

Some F1-teams use 7, others 6 gears.
The 7-ones I know are Ferrari, Jordan, McLaren and probably Jaguar; the rest uses one gear less.

I was wondering about the differences in length of the 1 gear. In case of a 7-box the 1 can be used solely as a starting gear; how short that is we all saw when Mika accidently engaged it shifting down for the first chicane at Monza last year and the rear end locked up completely.

But now the 6-box drivers: don't they need that 1 gear in the race too? There are some very slow corners on some tracks where they might use it or is that a wrong assumption?
If so they have to find a compromise between an ideal starting gear and an useful racing gear. But it would surely handicap their starting ability.

Where's all the gear-logic at 10-10s to shed some light on this? ;)

The ratio of the 1st gear will be approxamately the same, irregardless of the number of ratios available. The only difference will be the "gap" between each gear.

A seven speed box allows the engine to be tuned to a narrower power band, say 3000 useable, vs 3400 useable, which will allow for higher HP production. There will be a slight reduction in mechanical efficiency due to the extra inertia of the extra gearset, but that will be (should be, or it isn't worth it !) more than offset by the gain in HP.