Not a significant improvement. The RST isn't a great fork, but the Six is only like one step higher in quality.
I'd ride it like it is and save some money for a good deal on an upper end fork on closeout. I'd wait about a year, save about $150 to $200 and get a decent fork. By then, you'll know more about your riding style and can be a smarter consumer.
Plus, by then you'll have some experience at bike mechanics under your belt and we'll walk you through installing it yourself.
Enjoy!
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"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger