I am not sure what your horse's hoof issues are, but Farrier's Formula and SmartSox are completely different supplements and provide different benefits. Farrier's Formula provides healthy hoof growth, prevents cracking, and provides ingredients for healthy skin and coat, etc. SmartSox is essentially a pain-reliever. Horses that seem to have sore feet and heels, or are known to have poor blood circulation will benefit from SmartSox. Therefore, if your horse is just having soreness issues, and his hooves are in good condition with no cracks or flaking--then I would maybe reduce the Farrier's Formula dosage or cut it out. I myself just used SmartSox because my horse's hooves are in great condition but because of the navicular she was suffering from extreme heel pain.
If you are considering using Magic Cushion Xtreme Hoof Packing, that tells me your horse suffers from sore feet. So yes, I would use it before, during, and after a weekend of showing to prevent/reduce pain. I have never used this myself, but do believe in additional supplementing/treatment during times of stress (show weekends, traveling, etc).