Since frame rate drop and stuttering (on my PC anyways) happen at the same time, it's basically the same thing. BUT, low overall frame rate is a different issue.
Low overall frame rates are due to a slow CPU, a low end graphics card, or both. TSX off along with low quality settings can get a reasonable frame rate overall, but to me it looks like ........

So a fast CPU (over 3.5Ghz stock, dual core or quad core) and a mid- range to high range GPU gets the best results.
Frame rate drop/ stuttering is due to high resolution/ high poly count assets/ scenery on the next bunch of tiles loading into the game from the hard drive, as Professor Buzz said. Some have minimized this issue with a fast SSD hard drive, others say (along with my own testing on my rig) that an SSD doesn't help with gaming per se, just the initial load of a game or Windows. My hard drive is not huge (500Gb) and is kept clean and optimized so I don't get stuttering too bad.
And what I always say, about a new purchase/ new build/ upgrade, PC or lap top, is don't do this just for Railworks. Do it because it's really time to have nicer, better "stuff" that will be good for a while longer all around.

Ryzen 7 2700K, Asus Prime X570P, 32Gb DDR4, 2x 1Tb M.2 SSD's, RTX2060 6Gb, Occulus Rift
Win 10 Pro 64bit, keyboard/ mouse/ wheel/ pedals/ baseball bat
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