I was able to optimize the high efficiency reactor!
1,346 HU/t, efficiency 42.07 (1,370 HU/t, efficiency 42.81 continuous)
0B23120D0C0D120A122306230C0D0C0D0C0D12230C0D0C0D0C0D0C0D0C0D0C0D0C0D0C0A0C0D0C0D0C0D0C0D120A120D0C0A120D0C0D
(starting temp 6000, suspend on 6500)
I am fairly certain this still isn't the most HU a 40 eff reactor can make.
The only downside is that (most likely) the Reactor Control / Nuclear Control mod is needed, I always play with it enabled so I don't know if this reactor could be controlled by vanilla redstone.