Thanks for the tip, but adding --btc-address [insert bitcoin wallet address here] to the command-line does not change the picture. As said, cgminer 3.12.3 worked out of the box with these settings.
Solving this myself, the previous version did work without -o http:// . So to anyone who's wondering, running 4.3.4 successfully will simply require:
cgminer.exe -o
http://localhost:8332 -u something -p something --btc-address insertbitcoinwalletaddresshere