Alright... Now this is just advanced guessing, but: If your new monitor worked faster right out of the box, it may have installed the drivers automatically through the HDMI cable. That's a more and more common feature in USB so why not in HDMI as well. If not, the LG software certainly has installed the monitor drivers. Your old monitor may not have had any automatic driver installing feature and if you haven't installed the dedicated drivers for it manually it might not have given the full power. Generic Windows monitor drivers have been known to cause issues. Actually all generic Windows drivers cause issues sooner or later.
As for your card getting hotter it's perfectly normal given the fact of the card having to do 20% more work.
For viewing the instruments better, start with the automatic FOV setting and play with it until you find what pleases you. Your old monitor was relatively much higher, you're actually missing 120 pixels vertically. That's 10%. On my monitor 10% of the screen height equals the diameter of a gauge. If your FOV settings have been adjusted according to a 16/10 (width/height) monitor, they're way off with a 21/9 one.
