Are 30L Ortlieb Sport Packer Classics sufficient?

[canuckjgc]

I'm looking at buying the Ortlieb Sport Packer Classics (cheaper than plus) at 30L to use with an Old Man Mountain rack.

I will be doing a few out-and-back overnighters on singletrack with my wife.  I have to haul the tent, my sleeping bag and mat, stove, food and bits of other gear (remember for one night typically).

Do you think 30L will be sufficient? Is the pannier/rack combo ok?  I don't know the diameter of OMM and it's not on the website.

The next size up is 40L.

I want panniers for this trip rather than a true bikepacking setup.

[longman]

2 x 30L should be fine, you may have to strap some stuff to the top of the rack...tent, pad. I used 2 x 27L on the rear rack for the GDMBR with a 10L stuff sack on top of the front rack to balance the weight a bit. Without food one of the panniers was almost empty.