Have had a number of manual trans cars and the best gate I have seen is a five speed with first down and reverse up to the left past a detent and second through fifth in a "H". This is the best for spirited driving particularly with a low first used only for starting.
The next best is fifth up and reverse down in the far right again with a detent. This is good with a really long fifth (O/D) that is only reached in Interstate cruise.
No matter what you do with a six speed this requires four gates and can be confusing in a fast-changing environment (unless you have electronic paddle shifting with pre-selector as in F1. Then the gate does not matter). Suspect in the end, a paddle 5-spd (or 4+lock) automatic might be the fast way around.
In general you need more gears to make the most of a narrow torque band and with variable valve timing the band should be very broad.
The other alternative is a ratchet shifter but these can be annoying particularly if you want to skip a gear (often did for relaxed driving both in Fiero and Sunbird V-8).
For autocrossing, the fewer shifts the better. In the Sunbird I usually started in 2nd gear to avoid a shift 15 feet out of the gate and it only had a four speed "Muncie by Saginaw" (B-W 5 speed was not rated for the torque). Even so it had AWS at will - front with steering and rear with foot.
BTW considering reality, I would be very surprised if there is a production engine that puts out over 200hp. 300hp from a 2.4 is strictly for the race track and not on 87 PON with a 50,000 mile emissions warrenty.
Keep in mind that HP may determine the top speed but not how fast you will get there. For autocrossing what you want is a very broad and flat torque curve, something that variable valve timing can give you. Something else you get is greater tolerance for low octane gas than typical, and with a 3.50" bore (does anyone have the B/S of the 2.4, I could not find it but is probably the same long stroke as a 2.2 so increase is probably in piston diameter) VVT is probably a big piece of 10:1 compression since it has the ability to restrict flow at low rpm/high load. (optimization is not always for maximum flow).
As to the s/c version. First I should say that IMNSHO the place for supercharging is about 20,000 feet. That said it is very popular today and if the electronics can adjust for burn rate of the gasoline (what octane measures) then I would not be surprised to see the same engines used in the Chevvy Cobalt in the Solstice.
That means the 2.0 s/c engine, not a 2.4. EPA certification is expensive and the Solstice will be piggybacking on other car's certs whenever possible. You also do not need the complexity of DOHC for a s/c engine and boost tuning might take the place of the variable valve timing. Bottom line: particularly for autocrossing, I'd rather have the N/A engine & manual or paddle trans. Suspect the s/c might be available only with automatic.
One other thing to remember: the General never puts all of the goodies on the table at once. '65 Riv was what the '63 should have been. Fiero didn't get the V-6 til 85, the five speed til 86.
Even though Americans (and Europeans though they hide it) prefer automatics, the first cars will probably be all manual trans and the same color (remember the Judge ? Reatta ?), Resale Red outside and grey or saddle inside. Options limited to abs, a/c (might be standard) and sound. Possibly leather though GM cloth wears like iron, is cooler, and sticks to your pants better (serious autocrossers will install harnesses first thing - good harness can make 1/2 second difference in a run). Would like to see a Saf-T-Track option, would make up for the extra weight and make AWS easier.
There may be the reason for the suprisingly high weight: same EPA class as the Cobalt. Might also mean that there will be some easily unboltable but weighty items like the coctail shakers in a Corvair.
Just some thoughts.