I've been using Royal Purple since about 10k miles on mine. I'm just over 65k miles now. It is a good oil, but it is possible that it can remove gunk inside the engine. It would depend on how well it was maintained and what oils were used in the past.
Here are a couple FAQs from Royal Purple's site:
Can your motor oils be used in older engines?
Yes. Mileage and/or age is not a factor when used in a mechanically sound engine. In high-mileage applications, we do recommend running a minimum of two short (3,000 mile/5,000Km) intervals before extending the oil drain intervals. This will enable Royal Purple’s high solvency to remove existing deposits gradually; such deposits can restrict oil flow, if excessive, as well as reduce the oil service life significantly...
Royal Purple (and other synthetics) are not a recommended switch on a high mileage car. If you wish to run synthetics, it should be switched over early in the car's life (like 10k miles, as this guy did). Otherwise, you will have to do as RP suggests and have a few short intervals... and as expensive as that stuff is - that's a major PITA!!
But, I'm with Keith (05horse): conventional oil (Castrol for me), good filter (Purolator Premium), and regular oil changes (~3250 miles).
FLASH = 98 V6, chrome yellow, black & blue accents, 146k daily driver POWER
: divorced exhaust with glasspacks; BBK CAI, TB, UDPs; (shift kit in the garage) STYLE
: black headlights, black taillights, black grille, black hood pins, black window tint, blue hood & side scoops, blue billet fuel door, interior billet, 12000k HIDs RIMS
: XXR 006 black spoke with blue lip; 18x8.5 front, 18x9.5 rear TIRES
: BFG KDW/2 245/40R18 front, 275/35R18 rear