You guys should go to the first page of this thread, click the s2ki link and have a good read. everything's explained there pretty clearly.

it's not the gear teeth that get mushroomed, it's the synchro dogs that do because they have to absorb a greater force (greater spinning speed difference) when skipping gears.

migoreng, the if 3rd had the same ratio as 4th it's dog would get mushroomed too. that's kinda why it has the shorter ratio.

in any case, this problem seems to hit the 5th and 6th gear synchros the worst.

double clutching for skipped upshifts will allow the falling engine speed to slow the input shaft to the right speed for the gear you're skipping to, but you'll need to shift into it with the correct timing.

rowing through the gears as veyzzii said will distribute the speed matching load among all the synchros, which means no individual synchro will take the brunt of the force, but if you do this at normal shifting pace it's likely the engine speed will have fallen all the way to idle during the time the clutch was pressed in.

in all honesty I don't get it - if it's known skip shifting can cause accelerated synchro wear on the S, then regardless of the questionable synchro design, why do it? the car has a peaky powerband and a close ratio box with a dream shift action, it was made for shifting gears. it's not like it's a huge amount of extra effort anyway.

my 2c.