I also use a Tubus Cosmo. If you use the lower siderails, the load is lower still than the Logo. And it leaves the top available for a trunk bag.

Backrollers? Those are HUGE, you know. What are you commuting with? I recently upgraded to a pair of Ortleib Sport Packer Plus--a front pannier. I can fit a pair of jeans, four shirts, and a pair of sneakers in one, my snacks and lunches for the week and library books in the other, with some room leftover.

If you haven't put in the order already (I see you said "request" not "order") call and talk with Wayne at The Touring Store.com. Despite the name, he knows the difference between touring and commuting. He's never steered me wrong. And he carries Ortlieb and Tubus, both discounted from MSRP.

BTW, every non-Tubus rack I've ever owned (including some that are nearly as expensive) have wiggled and swayed under heavy loads. Not so much when commuting, but when I have the grocery panniers filled with canned goods and other stuff that's chock-full of gravity.