Personally dont like very small needles. Needles should be adjusted to the oil thickness IMO, I use 19 or 20G for nebido, 21 or 23G on glutes depending on how the oil flows, and 25g for rest of body parts, although I have used 21g on bicep due to lazyness lol.
Also not a very big believer in injecting very slow, not saying one should shoot the stuff but I inject over 3ml in 30 or 40secs. IMO pip has more to do with gear quality than how slow you inject it.