Best way to connect batteries?

I currently have 8 Trojan T 105s, wired 4 in series, with two parallel series in a 24 volt system.

Is this the optimal way to have them wired considering the two paths?

Also, they batteries are fairly new (4-6 months) and have seen very little use (less than 5-10% drawn down daily), and I wanted to know if adding an additional T-105s would be acceptable for additional available power, and how to wire them optimally. I'm not ready to make the jump to bigger batteries yet as I am doing an assessment of my expected daily needs and once I know it will likely be going with industrial batteries. But I am anticipating an increase in use and want more in reserve.

Thanks for helping a noob!