Thanks Steve.
I had not seen Discount Per Products Quantity contribution previously. Having just looked at the general contribution overview, it's not quite what I was after, but may be worth pursuing if I can't get my desired approach to pan out.
To make things simple, many products might share a similar price break scheme, but that is not a requirement. I liked the concept of the original QPBPP, but with the use of attribute pricing, not all product/attribute combinations were seeing the same percentage of savings (as a $10 item, with a $1 off 5 or more would be 10% savings, but if the same $10 product had a $10 attribute selected, the same $1 discount would be applied, resulting in a 5% savings). The use of actual attribute pricing further complicated matters, but was a necessity to address customer confusion in pricing. So, now a need to apply a quantity percent discount.
I did find that my use of $factor within the PriceFormatter was not being carried back to shopping_cart. For a php programmer, probably a "well, yeah" observation, but this has been some of my most in depth php coding short of merging contribs. By redeclaring it as this->$theFactor and then referencing it from within shopping_cart as $pf->theFactor, the value was available for use. I have some rounding issues that I need to address, and some more testing to ensure that the discount factor is applied correctly to items in the cart (and balances to the cart subtotal).
And, after seeing some other threads regarding discounts and their impact on payment authorizations (PayPal, Authorize.net, etc), I now know I need to double-check that aspect as well.
If any are interested, I'll post the in-progress modifications for review and feedback.