CaffeinatedOrange

What's your FPS at now and what mods are you running? You have an 850M; that's not a hugely powerful GPU. Tbh, you're probably expecting too much out of it.

Going with one great card is always the better choice than running SLI/Crossfire. Honestly, the latter seems to be more trouble than it's worth.

IMO, ESO just isn't worth the price. You can buy better games for 60 bucks, and save the money on the monthly sub for other games. ESO also has a... well, a rather large problem, last I checked, with bot players.

Reinstalling NMM might help. If it still doesn't like you, just install the USKP manually.

Add bBorderRegionsEnabled=0 under [General] in your Skyrim.ini to go check it out. c:

"What should I upgrade for better graphics?" Hmm... maybe the thing that handles graphics... ;) Also, I don't believe that Skyrim is quite as CPU heavy as you and others think it is. Sure, you need a decent CPU, but you don't need the most expensive one on the market. You didn't list out exactly what CPU you have, but from what I can tell that's quite okay for Skyrim unless you start running a lot of script-heavy mods. The main thing you should upgrade is indeed your GPU; I personally recommend a minimum of 3GB no matter what, but more is better. However... there is no benefit to running 4K textures if you're not going to run in 1080 HD or better. You just won't be able to see it. I think you're looking at the task of making Skyrim look better wrong.

Well, you can't install ENBs with NMM. Simple as that. If you can't handle doing that for whatever reason, there's this. http://www.nexusmods.com/skyrim/mods/7804/?

Updating to Win 8.1 shouldn't be the "fix" to a problem like this. That's not even a fix at all. Uninstall and reinstall drivers for your GPU, DirectX, and also try updating/reinstalling Microsoft C++. Make sure in your NVIDIA Control Panel that, under Manage 3D Settings, the preferred graphics processor is set to 'High-performance NVIDIA processor' and not 'Integrated Graphics' or 'auto select'. You've definitely got something wrong with your system in general; it could be a huge problem, could be a little hiccup.

ENB is a rather unoptimized software; I would think that's normal with Skyrim's engine being so finicky. It may also be that SLI is doing you harm instead of good depending on drivers, but I've little experience with SLI. FPS locking your game to something just under 60 FPS or your lowest drop would probably help make it less noticeable if that's a huge issue for you. Disabling V-sync may also give you a pleasing result as well. The SOS ENB also has depth of field, yeah? Disabling that might give you a little FPS, and you could add Dynavision to give you some DOF effects if you feel you need them. Although I do agree with Georgiegril; your system isn't weak or anything, it's just that Skyrim and its engine behave strangely and can be bothersome to get proper FPS rates out of. I do. :P

Textures are a dime a dozen, sure, but how many of them are actually good? And then how many of these mesh replacers / added creatures can be universally considered lore friendly? :P

Yeah, just look at the mod's description page and check if it's compatible or has a patch. I have two mods to recommend: Weather Patch - http://www.nexusmods.com/skyrim/mods/39799/? Someone added upon/improved COT and did one hell of a good job at it. The below mod even requires this so you can use the both of them together. However, Realistic Nights is EXTREMELY dark; it may not be your cup of tea, so this is a very good alternative and is similar to COT in that it has different levels but they are not "sun glasse'd"; it's very well done! Realistic Nights - http://www.nexusmods.com/skyrim/mods/49472 Quite nice from what I can tell so far. Only messed around with it for about 10 minutes though.

BOSS 3.0 / LOOT seems pretty okay to use for the most part, but if you aren't using any mods made this year, I don't really recommend it. I got some CTDs after using it, but I believe that was 100% unrelated, save for possibly SPIKE.esm being placed before Update.esm. I'm not allowing it to do that, and I'm not using any new mods and I've used the new load order from it for a few hours now and everything seems great. I'll be messing with it for at least another week before deciding for sure whether I like it or not, though. My main issue so far is how messy the load order is. One .esp of mod might be at the very top of the order while the other .esp is at the bottom of it; ugh, so unorganized. LOOT works completely differently than Boss 2.1/2.2 does, though. BOSS 2 is very rudimentary and is basically a sorting software, whereas LOOT actually looks at all the mods and decides where to place them by seeing what they do, from my understanding. Also, BOSS 2.2 is using the same masterlist that 2.1 is/was using, from what I can tell, so that means the masterlist hasn't been updated since around mid-January. Unless I'm terribly misinformed and have somehow managed to miss this information for 1/4 of a freaking year.

Holy freaking dead topic bump. SGTM can be found here; http://www.uesp.net/wiki/Skyrim:Console

There's this. http://www.nexusmods.com/skyrim/mods/8808/? Not sure if it's still working well, though.

Disabling other mods mid-game like that is going to cause problems, not fix them. Anyway, not entirely sure what this could be since it doesn't sound like a memory issue. You'd probably be better off asking at the Wyrmstooth comments section.