For Beef Sticks I'd try and stay around 80/20. You don't want it too far or they get greasy.
Sausage is different, usually straight pork shoulder butt will make half way decent sausage, they are closer to 78/32%. I prefer sausage around 75/25.
Summer Sausage, thats a different animal. You want closer to 65/35% or even 60/40%. You only want to cook it low and slow around 160F and do lower finish temps but hold it longer for the lethality. For instance I follow USDA Appendix A in which I cook mine to 135F and a hold time of at least 40 minutes. You don't want to render the fat, thats why the lower temp and a hold temp. At about 145F they can start to render, and different fat types render before others.
Now I use a calibrated thermometer for all my cooking.
