Mandrel bender tooling - what size to order?

Hey, gang, I am getting ready to order more tooling for my mandrel bender. I already have 1.625" (1 5/8"), 2", 2.5" and 3" (all for stainless, aluminum and mild steel), and 2.25" is on the way.

For header work, I need to have a size between 1.625" and 2" but I'd rather not spend the mucho $$$ for both 1 3/4" and 1 7/8". So, I'm asking for advice: which would better support your needs for high-performance header applications, 1 3/4" or 1 7/8"? Or are the applications so specific that you'd recommend both sizes? Also, do you see much need for 1.5"? :confused:

Thanks for your input!

Hank