Why can't I set 1680x1050

Did you upgrade from something? When I upgraded from my 1280x1024 standard non-wide 19 inch to my wide 22inch some games like DMC4 did not immediately recognize the new screen and thus did not add the new rezs so I also had to do some searching.

Anyways these sound like old games so not all of them support widescreen but the widescreengamingforums may be able to help you further on some of them (not too big on MMOs though).
WSGFWiki

Here's the report for Sacrifice including how to add widescreen support.
Widescreen Gaming Forum :: View topic - Sacrifice: Detailed Report

Here's the ini tweak required for Generals (although as the game is Vert- you may wish to instead rely on either letterboxed scaling by your graphics card's drivers or if your screen has 1:1 pixel support on that feature (LG screens for instance have a 4:3 in wide button))
Widescreen Gaming Forum :: View topic - Solution: C&C: Generals & ZH [Edit] [Hack]

....a driver won't add resolutions to a game which the game does not support

once again that will have no effect on the res available within games.

Which I linked him to.

The Last Remant is a new game thus it supports Widescreen.

However old games like Sacrifice and Generals + Zero Hour don't support Widescreen, only 4:3 and 5:4 Aspect Ratios and thus require those tweaks I linked you too.
It seems you have me on ignore or something though as you're not acknowledging anything I say which is fine by me as it's your loss.

You're welcome

Battles of Middle Earth 2
Widescreen Gaming Forum :: View topic - Middle-earth II & Witch-king: Detailed Report

Battles of Middle Earth 1
Widescreen Gaming Forum :: View topic - Battle for Middle-earth: Detailed Report

Titan Quest
Widescreen Gaming Forum :: View topic - Titan Quest & Immortal Throne

Warcraft 3
Widescreen Gaming Forum :: View topic - Warcraft III: Detailed Report
(I assume the same would apply to the expansion)