That tube (xx1610) is actually the first of Super Second Generation (aka, Supergen) to be developed... They improved the hole ratio to around 75% in the MCP and used quite a few other tricks too... At the time, it was roughly equivalent to the Gen3 of the era.
I've been waiting to see one of those

Is that one of yours Flex? I'd love to know how it performs visually -
David.