Here is everything you need to know about setting up the GM ESC:
http://www.rctech.net/forum/7908081-post1851.html
Use Martin's settings file, tweak the 4 settings in the guide to:
Switchpoint 10,000RPM
Fixed Timing 25deg
Amp Limit 80degC
Motor cutoff temp 120degC (not sure if the Reedy has a temp sensor in it, so this may not do anything).
FDR 6.5
And enable 'Variable Dependence Timing' and 'High Speed Timing from Switchpoint'
And leave the endbell timing at its neutral position.