I don't see any reason in using Mobil1 ESP, I can't see the benefits of using a Low SAPS oil in a MPFI engine that doesn't consume much oil, if what you're doing works keep up with it, I see know reason to change and a resource conserving 5W30 should be more than thick enough, so many of these engines last forever on Toyota's recommended Xw20 that probably doesn't get changed as often as you change your oil, If you're using EP, I'd probably run it a year instead of 6 months sounds like you drive less than 10k a year, if you're gonna dump it every 6 months with less than 5k on it just use supertech or whatever you can get off the clearance rack for cheap.