TimTam :P

CPU Architecture, Memory & I/O systems and host controllers. The entire deal. There are limits for how fast the system can move data within a given type of data movement. (That's why SSDs work over HDDs for loading things quickly.) 
 
Then you have to deal with the way the specific program is asking for Data. When this type of issue crops up, going up in resolution normally sees very little drop off in FPS because the bottleneck hasn't really changed, even if more information is demanded. You're also playing a game that leverages huge amounts of memory, so it's going to be really sensitive to certain aspects. 
 
Without some really extensive benchmarks, it's hard to say exactly where the bottleneck is, but, looking at some information on the game, it probably in the "you'd need a lot more CPU cores". Which goes back to the I/O is probably saturated.

ohh okay so its a 1070 thing... might get a 1440p monitor soon then  
thanks man

yeah but the only available ones are conventional ratios... I'd need 9:41  I don't think that's normal lol

https://www.beamng.com/resources/hirochi-prasu.2251/

Haha its gotta be the Sunburst or the Prasu! They're so fun to drive especially with a couple of mods.

250-300 max

You migh want to part it out. I'm selling off a significantly older rig than that, and I discovered that the motherboard for my system sells for nearly as much as the system as a whole. 

well I wouldn't pay more than 200$ US. google says that's 250$ AUS