I have 5000 mi on my new superstroker so far. Just bought 16qts of 10w40 Royal Purple at $3.99 each. I previously purchased 3 gal jugs of Delo 15w40 and currently using that. Now after I switch over, if I still have any 15w40 Delo 400 left, can I top off my Royal Purple with it. Plan to do 6-8k oil changes with a filter change in between. BTW, I can't wait to feel the xtra engine smoothness everyone is mentioning when switching to RP.