I'm not fimilar with the Duratrax ESC's or the SpeedGem motors I run Orion Motors & LRP speeders but I hope this helps you & maybe someone else.
I copied this from a post I made on McCulloughsrcracing.com
1. - Timing marks on a can are only as accurate as the guy putting the decal on the can, but when the decals are installed they can not be way off or they would cover vent holes, but I would still recommend a timing jig.
2. - Timing for differnt classes are ( as I remember but I could be wrong )
4wd - 6*
truck - 12*
2wd - 18*
3. - I have seen guys run motors on lathes & break in mode and keep the endbell a little loose & twist it until it sounds "right" I usually set it like the chart above & advust it ffrom tere if needed
4. - I know doug has ran mega high timing & gear the motor down & I think that really would have made a difference in the past but now with the motors & batteries available every class (except maybe 4wd sometimes) has more power then needed. I adjust gearing more then timing.
I really can't remember the gearing but I think this is close
4wd - 5-7 over the wind
truck - 7-9 over the turn
2wd - 8-10 over the turn
If I'm running a 15t pinion on my 4wd which is on the lower end (10x2 in a 4wd would need between a 15 - 17 tooth ) and I still needed more power I would adjust the timing ( I have also adjusted with brushes & springs )
5. - I'm not sure if there is a limit to how far you can go but I would never push it to far past the chart. but I tend to be safer then some others.