"HD" depends on what textures you use on your models (models are calculated with vertices, so dont depend on resolutions). using hd-textures for everything will kill your game and framerate, you need a lot of experience to know wich texture can be low or high (depends on level-design, spotpoints of the player, modelsize etc.). shaders are always usable for HD or not, doesnt matter, just depends on the textures they are used for.
fpsc scales the HUDS and displays up from 1024x768, you cant do anything about that, except not using any HUDS or only small, cubic ones to not show up line-irittations. that is not the case for the v119-compass/radar, wich are not scaled, whatever resolution you choose.
to change screen resolution in the buildgame, simply add "height=x" and "width=x" to the setup.ini of your final game (doesnt work for testgame, has to be a multiple of 2, like 1920x1080).