What is making mg gaming pc lag? a bottleneck?

Update:

Yes, skyrim does run fine without the mods.

Additionally, I have been running my gta v on ultra settings and my gpu memory usage is reaching to 2900-3400 mb. on gpu-z the gpu load is anywhere from a 30-75% (increasing during car crashes, shooting etc. the cpu is running at about 40-50% while about 7gb of my 16 gddr3 are being used.

i had also tried turning down the settings with no prevail as lag spikes still persisted.

i should also note my hdd drive seems to be spiking extremely frequently on 'respurce monitor'.

this is even more frustrating when ive found my friend has recently gotten a new pc with the following specs...

Intel i5-6600K, Radeon R7 370, 600W PSU, 16GB DDR4 Dual-Channel, 250GB SSD & 500GB HDD

...yet she is running the game on ultra with 90fps and only using around 500mb of vram memory (without overclocking).
however, she has told me she has up to 8 gb of shared memory while i have only 3 - not sure if this is a contributing factor.

again thanks for the help and any explanation as to why im having these issues - and why my friend is able to have much better performance with a (according to her) inferior graphics card to my own.

So with skyrim once my vram usage starts getting into the high 3000 mb is that when should start toning down the mods?

also, i very recently launched gta with the same settings as my friend yet she is still yielding better fps. however her vsync was off at the time. but it is concerning to see that my graphics card (which i had thought was better) is being out performed in regards to how much vram is being used by her (only around 500mb supposedly) compared to me (3000's mb range).

as you suggested i will try some lower settings to see if i get a boost in performance. but would there possibly anyway she is achieving better performance with a worse video card? for example, could her gpu be automatically overclocking or likewise the cpu be overclocking automatically?

lastly, would you recommend i get an ssd instead of a hdd (and a better cooling system as the only cooling in my pc is built onto the gpu and cpu) to improve performance?

ill have to ask her how much vram was being used exactly although i know it was significantly less than mine and im sure she was running the game at 1080p - "all settings maxed" as she told me many times.

as for the tips you gave me they seemed to have worked.

firstly i played gta v with all advanced graphics settings turned on. i also used gpu-z which said my 'memory used' got to a maximum of about 3500mb whilst my 'gpu load' got to a maximum of 99%. however i do not know how long it was on 99% (i think it was only for a small period of time ) as i had set the gpu-z to show me the highest it goes. in regards to fps i was running a solid 60 frames with fully maxed out settings but i did drop from 10-30 frames when crashing my car, police chases, or going into highly populated areas.

i then turned off all the advanced graphical settings as you suggested while keeping all normal graphics turned on ultra (aside from msaa and msaa reflection - side note=which my friend also does not have turned on) and i seemed to stay at a stable 57-60 frames per second. my 'gpu load' went from anywhere from 40-70% while the memory used only decreased slightly going to about 3400-3500mb.

are these numbers, regarding the memory usage and gpu load, damaging to my pc? the 99% im sure cant be a good thing correct?

also once again regarding my friend, are there any other ways she could be running this game maxed out while only using around 500-100mb of vram in 1080p - or is this not possible? if not,, could she be viewing a the amount of vram she has remaining rather than what she using? she had also told me her gpu load was only in the 30-40% range which again seemed strange as i had thought i had a better pc than her?

lastly, is my pc as a whole and graphics card alone sufficient enough and capable to run these newer/future games on high to ultra like gta v or am i being to hopeful?


Update

Hey bicycle, would you also be able to tell me why my gpu load is in the high 80's and my fps is dropping to 50 now especially with in the desert area. is it normal for my gpu to have a load of 90% and to be using 3.mb of vram memory on gta v (with settings on high to very high - not ultra? or is my gpu broken in some way?

Yes, but i was still recieving a 99% gpu-load with my graphics settings on high? this is strange to me as i had though thr 980 could achieve a very high setting easily?

so settings that can be potentially gpu taxing can vary from gpu to gpu?

but i would though my gtx 980 would have been able to handle gta v on ultra?