I've admitted defeat with the TSW framerate problems and weird issues. There's a dovetail sale on at their store at the moment so I picked up the TS2019 UK pack and a load of DLC, plus the RWenhancer pack, and Armstrong Powerhouse track and weather packs. Tweaked everything to max settings (quad core i7 and gtx 1080) and set nvidia v-sync for railworks64 to on permanently. The result is very close to TSW in terms of visuals (4k and the enhancement pack are a great combination), but with awesome framerate, cab sway, longer routes, 3rd party add ons, sounds are good, massive choice of locos and routes. Should have done this ages ago. Recommended if you have the kit. Its not as intuitive as TSW but I'm already so glad I made this choice.