Can anyone elaborate on what performance would be like if I was to switch from my 1680x1050 res monitor, to a 1920x1200 24" screen? 
 
I am currently running a GTX 275 and get excellent frames in almost all games, minus the usual resource hogs. 
 
Suggestions or experiences are welcome.

Well X1050 is no big deal, neither is 1080p, which is slightly slower than X1050. If you go to benchmark sites, they always show three benchmarks, X1050, X1200 and X1600. Usually you will lose more frames, that's because it's really rendering more graphics. Your videocard shouldn't have a problem with X1200 though, it's will run well enough. Maybe certain games like crysis, or more demanding games you will notice a few slowdowns. Alot of the time, those running it at higer resolutions does use sli. Not only does that give you more video memory, which is good, it also gives you more framerates.

There will certainly be a performance hit, depending on the game and the settings you're currently using. You may have to drop down a few settings to make up the lost FPS.

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Well X1050 is no big deal, neither is 1080p, which is slightly slower than X1050. If you go to benchmark sites, they always show three benchmarks, X1050, X1200 and X1600. Usually you will lose more frames, that's because it's really rendering more graphics. Your videocard shouldn't have a problem with X1200 though, it's will run well enough. Maybe certain games like crysis, or more demanding games you will notice a few slowdowns. Alot of the time, those running it at higer resolutions does use sli. Not only does that give you more video memory, which is good, it also gives you more framerates.

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Well obviously your frames are going to drop. Try looking at some tests at Tom's Hardware or something. Usually they test a variety of resolutions and several games so you can really see all the possible differences.

Would it be worth it to go 1920x1200? or just 1920x1080? 
 
Keep in mind I do sometimes run my PC through my 1080p TV and do not see much difference in FPS at all, in fact sometimes it seems to up a little more 0.o

1050 to 1200 is actually a much bigger leap than you might initially assume (1764000 pixels vs 2304000 pixels).  1680x1050 is a lower resolution than the old 5:4 mack daddy 1600x1200, the performance hit can bit pretty noticable depending on the title on lower end hardware.  That being said the 275 will handle it just fine.

I'm using a 1200 monitor right now with a 5850 which is slightly less powerful than your 275.  Increasing the resolution your monitor is running does lower your FPS but on 99% of games there aren't any noticeable performance drops.   
 
I haven't noticed any performance drops with stuff like Just Cause 2, TF2 or SupCom 2.  Honestly Crysis and Napoleon Total War are the only games I've noticed any performance drops when upgrading my resolution and even then it's not like games are unplayable or anything.

Get the 1920x1200 and turn the resolution down in games that cause you any issues.

GTX 275 is a good mid-high end card that will play most games at that resolution just fine. You will just have to vary your AA settings, but it should be able to handle 4x in most games while at high to highest in-game quality settings.