Help with panniers

Hi! I have a Triban RC 120 and I’m commuting around 40 km a day (to and from work). I’ve been doing it for about a month and a half and I’m really enjoying it. The thing is, I always carry a backpack (around 4–5 kg with clothes and food), and although it’s manageable, it’s a bit uncomfortable.

I’ve been thinking about switching to panniers. I already have the Elops 500 rear rack from Decathlon, but I’ve never used panniers before, and I’m not sure if they would slow me down more than the backpack or if they’d actually be better overall.

Does anyone have experience or recommendations? Would panniers improve comfort and balance or just add more drag?

Thanks!