There is a way to only request RC5 packets (although the OGRers here would still want you to do both if possible... 😉). The work is assigned randomly between the 2 projects when both are left enabled.
In the config, you would need to change your project priority to be:
RC5,OGR=0,DES=0,CSC=0
That is, choose:
Option #2 - "Buffer and Buffer update options"
Option #9 - "Load-work precedence"
And change it there.