Cardarine and SR9009 are the two best SARMS you can take for endurance.
Cardarine and SR9009 are PPAR up regulators. Cardarine/SR9009 increases the expression of genes involved in the expenditure of energy, stimulates glucose uptake in skeletal muscle tissue and burns fat by stimulating fatty acid oxidation.
Both are great options and will significantly increase fat loss and endurance. Cardarine is slightly better for endurance and SR9009 is slightly better for fat loss.
If you want to just use one or the other -
The recommended dosage of cardarine is 20mg/day
The recommended dosage of SR9009 is 30mg/day
Cardarine has a half life of 24 hours so you only need to dose it once per day. Due to SR9009's short half life, you want to split up your daily dosage into 3 dosages throughout the day.
If you want to stack the two - I would take 20mg of cardarine with breakfast and then take 10-20mg of SR9009 about 1 hour before your workout.