I got this game in a bundle pack (store-bought DVD) as a gift from a friend a while back, but I can't -really- play it; either the resolution in full screen doesn't quite fit so I can't see the whole screen or access all options, or I play in boxed mode and can't scroll to the edges.

Does the GoG version correctly fit modern screens? Specifically, I play on my TV, a 42" plasma HDTV using a GeForce 560Ti card. I'd like to get this from GoG if I'll actually be able to play it (and probably all the other games from that bundle since they all had the same problem: Baldur's Gate 1 & 2, Icewind Dale 1 & 2, a couple others I hadn't heard of).

It does, but you might be able to get your copy working by installing the widescreen mod. IMO you should apply that anyway, along with the bug patch mods. See the mod guide at the top of the forum.

I don't believe the GoG version will help you any.

The nVidia Control panel offers scaling and positioning options for the desktop

if using the widescreen mod make sure you get the hotfix
http://www.shsforums.net/topic/37824-please-report-crashes-here/page__view__findpost__p__534260

right-click torment.exe and from the compatibility tab select the Disable the High DPI scaling option

you may also wish to try DxWnd
http://sourceforge.net/p/dxwnd/home/Home/