Have always used full synthetic oil in the VTX, various brands, Mobil 1 Automotive, Diesel, and MC 4T, Rotella T6, and I used Royal Purple in it once when I first got it. Always changed oil and filter at about 5000 miles until the last change. Have been using Mobil 1 10/40 Racing 4T for a few years now. Since I usually put about 4000 miles a year on the bike, I change it at 8000 miles now or about every 2 years and the oil still looks pretty good. Have used several different oil filters over the years, NAPA Gold, K & N, Honda and Supertech. I pretty much use Supertech ST6670 all the time now. AFAIC the $2.50 Supertech oil filter does a great job.
2003 VTX 1800R