I don't use the tranny trick, never have, and I don't see how useful it would be because you should be tuning your gears depending on the corner speeds of the track, but then, of course, you still have to compromise.
I'll try it one day, I guess, just to see if it really is effective, but in the mean time the way I tune my transmission is by making sure I can drift around certain corners without hitting the limiter.
So, I'd go to Grand Valley and make sure I can drift around the first corner in 2nd or 3rd, depending on the power of the car, at about 120-130 withouth hitting the limiter. Then just fix up the rest of the gears in the same way, making sure I dont hit the limiter midcorner around the rest of the corners on the track..
First, I'd change the Final Gear to around 4.4 or higher for lower toque cars (ie Japanese cars) or around 3.6 to 4 for high torque cars (v8 muscle), remembering that changing the final drive also effects the top speed of each gear.
You need good throttle control whilst drifting so find your balance, but of course the same technique can be applied for grip driving. If the car spins out too easily or breaks so much traction that you need to slow down too much to regain grip after drifting a little, tune it down (lower number). If you're bogging down or find you can't break traction as easily as you'd like, tune it up (higher number).
I think some people neglect how effective the final drive can really be for car control. Just my opinion, anyways..
Generally, max speed in each gear would be (km/h):
1st : 60-80
2nd: 110-135
3rd: 140-165
4th: 160-190
5th: 210-240
6th: 280-max speed just before it hits the limiter on the GV straight
3rd to 6th are off the top of my head but they sound about right..
Good luck dude.. 👍