On filters, the NAPA Gold Series is supposed to be equal to the Mobil 1 filter, with everything else inferior. This is based on extensive tests some guys did on all filters available for the XJ. As I recall, the main point of failure was that all the other filters at some point would allow the pre-filtered oil to mix with the post-filtered oil, so that some oil did not pass through the filter on every cycle. Frams were the worst, but I forget the rankings on the others in between. Bottom line was NAPA Gold part #51515 was the best value, costing less than half what Mobil 1 filter did. (That's XJ part number - does anybody know the NAPA Gold oil filter number for KJ's?)
IMHO, buying the absolute best oil and filter is a very cost-efficient investment; likewise plugs and wires and dist cap. Look at total costs over 200K life. Gas is by far the biggest number: at 17 MPG and $3 gallon (future gas price over 5-15 years), gas will cost you $35,290 for 200K miles. At $4/gallon, $47,060. By contrast, if you spend $50 per oil change for syn oil and best filter and change every 6K miles, that's $1,667 total over 200K miles, or less than 1/20th what you'll spend for $3 gas. Bottom line - buy the cheapest gas, but the most expensive oil and filter.