For reference I use 1.5” 23ga for glutes. If your goal is intramuscular injections than 5/8” is a little short. Smaller pins take forever to inject but to each their own.
I use 1-1/4” 27g and only takes 5 seconds to inject .3ml
I don’t know what your protocol is, but a lot of guys don’t tolerate SubQ injections as well as IM. So if things don’t feel right, that might be something to consider.
If I was going to recommend a protocol, I’d have you start out with IM injections and try SubQ later if you feel like you want to try it. I would also agree with @ncsugrad2002 and give delts a go.
when doing weekly or bi-weekly injections, i used 22 or 23g 1" for IM in quads. Having switched to daily injections i have a variety of 25 and 27g (1/2 - 5/8") for IM delt injections.
larger gauge you will feel less, but should push slow due to injection pressure.
The main difference for me is not so much the injection difference but the draw up difference. With the exception of systemlord who is injecting a drop, i don’t have the patience to draw test up with a 29 or 30g insulin pin (especially if you are drawing 0.5mL or more). If you want to stay IM in glute, i would say 1" would be minimum; delts and quads can get away with shorter and still be IM. Just my opinion though.