I'm taking 30, and my doctor told me that's that max they can prescribe. I'm ~175lbs, and this seems like the right amount for me. I have really high tolerances to other substances, like alcohol, and caffeine, so I expected I'd need a higher dosage, and we arrived at 30 pretty quickly.
Having a smaller dose to take later in the day sounds nice. I often feel my meds wear off a few hours before bed, when I'd like to be focusing on a hobby, which I'd love their help on. I think I'll ask my doctor about breaking up my dosage into two at my next appointment.
If 10mg feels like it's working for you, and you think the 5mg boost will be enough, stick with it and don't worry about comparing to other people's dosages. For me, my meds working feels like more energy throughout the week, and more ability to focus on and start tasks that otherwise could have bored or paralyzed me. I'd recommend you focus on getting to something like that with your meds if you can, while minimizing side effects (I've only ever had some slightly increased emotional volotility in the first couple weeks I first started n Adderall).