Some base oils (particularly group IV PAO) have difficulty dissolving additives in solution. Group V base oils like ANs and esters have low aniline points and high solvency which, when added to a non-polar base oil, improves the ability of the base oil blend to dissolve additives into solution and keep them in solution. In much the same way, they can dissolve carbon deposits, sludge, and varnish into solution as well, thus improving the oil's ability to clean inside the engine. They also have a positive effect on the oil's volatility, and improve the oil's shear and thermal stability at high heat. A downside is they can hurt low temperature pumpability as they tend to have low viscosity indexes of 80-100. They can also interfere with anti-wear performance if the concentration is too high.
HPL's oils contain both AN and ester. They clean better than M1 ESP and likely less volatile. Aside from the base oil, HPL employs much more top treatment with moly-based additives for better friction reduction and oxidation resistance, a higher amount of overbased detergents, and much higher starting TBN nearly double that of the M1 ESP.