Africa and the Middle East, because the major fronts if peace is not established. Perhaps with stronger German backing, the Ottoman Empire is able to fight back against Arab Revolution. Logistics is one thing, and IMO that would be dependent on the stability of the AH empire. The British would have to act fast in the Middle East and in Africa. Lettow-Vorbeck suddenly becomes an actual threat - if he can link up with German Field armies, they could cause some trouble.
I also wonder what the other allied parties would do in this scenario - (Japan, China in particular). The US, China and Japan are already placed in an unlikely alliance. I'd wager the US would fight on after the unrestricted submarine warefare and Zimmerman telegraphs. China may actually join the CP to kick out the foreigners (IOTL they had relations with CP till 1917 when they declared for the allies). If China does, you have the second sino- japanese war occurring early and that puts the US in a somewhat strange position.
Another effect of CP victory in Europe would be how the Austria Hungary Empire fairs. Does the defeat and probably annexing of parts of neighboring Italy, Serbia and possibly even Russia mean it survives its internal strife's? I'd wager, the ethnic problems may still stir up, but are unable to cause a complete dissolution of the Empire. Ofc this is also highly dependent on this problem that all of Europe would be facing.
Food. Where will they have enough to feed everyone? France and Germany were already starving, Italy relied on outside help and with the British blockading everything, it becomes a real issue. I thought about Russia providing, but it was a whole other powerkeg going off. Germany would have to have sufficient troops in Russia to make sure the *right* side (the side that is more lenient towards Germany) won, a difficult task (western intervention in IOTL failed to give the white army victory), to prevent a second front breaking out again (assuming the middle east becomes the main front after Europe). This also means Germany is overstretched and would probably result in German defeat in the Middle East.
Overall, I believe a peace agreement would have been the best option for Germany. They had the military, the only problem was that they didn't have the resources just yet. The allies would also fair well from one, whilst they sort out they all sort out their own issues from potential butterfly effects mentioned above. It seems likely Britain would get off scot-free until the next war is induced, in which case, it would probably have to fight Germany again.
Here is a crazy thought, Mexico sensing a CP total victory, declares against US. (ASB territory - but who knows).