Ron you have a racing engine, that's what an XS is. JMHO, Fishfreq's standard Optimax won't benefit from using the same oil not to mention Mercury specifically states NOT to intermix any other oil with racing oil. Direct from the FAQ:
It you run out of racing oil, you can't just "top off" with DFI or Premium Plus. However, since DFI and Premium Plus are completely compatible with each other, they can be intermixed at any time without concern.
I use the oil Mercury recommends for my engine (DFI) and do so with complete confidence. Spark plugs aren't $18 (or more) unless you're buying from Mercury or some other higher priced seller. I buy direct from one of NGK's "
oldest and largest US distributors" for under $12ea with the confidence I'm getting genuine NGK plugs from my engine.
That said, I
fully respect those who choose to buy plugs from their dealer or other Mercury authorized sellers to get the one year parts and labor warranty. I simply don't see the value for my 11yr old standard Optimax.
The bottom line for anyone is it's their engine, their money and I advocate one do what makes THEM happy. If that means using racing oil and spark plugs purchased from your dealer in your standard Optimax, ProXS, or racing engine then full steam ahead.