What currency? USD AUD etc..

Also what other system components do you have? If you don't know download speccy and try and find out what case you have. Make and model.

Most importantly, need to know the make and model of your PSU so we can know what GPUs are compatible. Case doesn't matter too much, but some GPUs won't be compatible with certain cases so case make and model would be useful too.

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but yeah im tryin to run games on ultra
and for some reason my Disk is at %99-%100 alot
i can hardly play this game cause it has lag spikes bad.
my budget is from $100-$200 USD im looking for around $150. tho
my Power Supply is 750W

The wattage of your PSU is next to irrelevant, it's the quality that matters. Since you're running a GTX 780 though, it's pretty safe to assume it's at least decent quality. Any GPU you're going to buy now for about $150 is not going to perform any better than your GTX 780 anyway, at least not enough to justify spending $150-200.

I'm guessing by "my Disk is at %99-%100 alot" you mean the HDD. Add an SSD and it will definitely help. Maybe add another 8GB RAM. Just grab another 1600MHz 2x4GB kit of the same design you currently have.

As for SSD, one of these would be a good shout;
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