First post, by truth_deleted
The S3 emulation code (including the VGA parts) is complex yet robust, a testament to the hard work of the DOSBox authors and others. It also seems robust as a PCI device in DOSBox+Win95 guest, but this achievement would have been less tested.
Changed the PCI Register values in pci_devices.h, according to documentation on S3 and PCI Registers. These changes are pertinent to DOSBox+patches* running a Win95 guest (* V1 and 9x patches; although the patch can be parsed when the V1 is not included). The result is good stability along with a very substantial and noticeable improvement in video lag, including better mouse cursor control. Tested UT99, Quake, and others. These hardware accelerated games are now playable even under low framerates. One of the changes, for instance, was to remove memory mapped I/O from the S3.
These tests were done while IDE was active (one of Codeholio's great contributions). Also, while testing, it's recommended not to drag the DOSBox window while loading UT99; I believe this will cause an issue with or without this patch, and is probably specific to 3dfx games.
Edit: see post further down in this thread for latest version.