brief instruction for 1.6.1:
Download source from here file: mingw32-libwebkitgtk-1.6.1*.rpm (opensuse's patch included)
With 1.6.1 we can use msys-perl 5.8.8 instead of strawberry's and none of my patches below except datadir.patch applicable. At maximum configuration (without geolocation) we can use:
configure --enable-mathml --enable-link-prefetch --enable-animation-api --enable-register-protocol-handler --enable-web-timing --enable-datagrid --enable-page-visibility-api --enable-3d-rendering --enable-image-resizer --enable-touch-icon-loading --prefix=/c/GTKDEVEL --with-gtk=2.0 --with-target=win32 --with-unicode-backend=glib
which require additional gstreamer, in my brief test it gain score: 100 on ACID3 and 296 on http://html5test.com. However there are some regressions: annoying text/image flickering and several widget misplaced also plugins still not implemented yet. Best gtk to use with is probably 2.24.8.
To shrink the runtime dll size to around 40% smaller, force the use of -Os flag (need to manually edit Gnumakefile) or disabling SVG/video will reduce size significantly.