This is what I do as well. I draw the oil from the vial using a 23g, and then inject with a 25g. For the first 15 years or so I always used a 1.5" needle, but I had some 1" needles that I didn't want to throw away, and they also seem to work just as well for a glute injection.
Glad to see somebody else on the boards say this. Other than slin pin size, 25g seems to be the common choice, but I can feel the difference pushing the plunger with a 23g or a 25g. I'm not after a faster injection, but I am after less needle shake when I use certain sites. Trying to minimize the inevitable scar tissue as I go on. I acknowledge tissue damage can vary with needle size OR with needle shake, but some of my shots can get pretty shaky with my old man shoulders ... gotta play to my advantages/disadvantages.
@Traork1 ... you asked about needle length too. I have used 1.5" but don't see the need unless you have some fat over the muscle you want the IM shot in. I don't do big shots, so I buy 3cc syringes with any length 21g pin attached to draw, then switch to a 23g 1" pin to inject.
I use Easy Touch U-100 insulin 1 cc 27 g 1/2" so does the Mrs. Works fine with oils, for some reason this brand draws and dispenses really fast compared to other brands. Use ventrogluteal hardly feel it. https://www.healthwarehouse.com/-2724852.html