I've been using a v2 pen with a 29 gauge .5" pen needle and it works great for my TRT. Nearly the same speed as a peptide through a 33 gauge.
That said, my test C is in GSO oil which is relatively thin and I warm my pen in a baby wipe warmer the night before a shot. If you use cottonseed oil at room temp it might be more challenging. YMMV
Edit to add: There are some potential concerns around degrading rubber pistons from contact with the oil. I can't visually see any evidence of this happening in my cartridge, but something to be aware of. I'm contemplating leaving a little oil in my cartridge when I'm done with it, and sending a sample to Jano after a few months of it sitting.