I’d say the stock front forks are competent enough and the stock rears are pretty bad. With this swap, i’d say it pushes the rear shocks to something a little bit more than competent (and even better if you purchase the formula 390 rebuild kit). http://formula390.com/formula390/parts.pl?D=dukeSuspension
I don’t plan on tracking or upgrading the front forks so my reasoning is this: I’d rather have competent front and rear (less than $50) OVER a competent front and overpowered rears ( $500+ and at this point you’d probably see the shortcomings of the front forks which you’re probably going to want to upgrade soon after).
I just came back from canyon carving. a little over 75 miles of 3-5 gear turns and plenty of 80 mph straightaways. I can definitely feel a positive difference.
@JohnnyLightning, slightly higher seat height. Someone on the rc390 threads measured out that the r6 shock was 5mm longer. Adjustment is all external. preload, rebound, and compression. Im 100% sure the reservoir would slip through towards the right side of the chassis without issues if the cat was lower and since it’s right side up, you wont need to cut anything.
here’s a photo on a 390 duke
this is what i trimmed to make it fit upside down. (that photo is of a 390 duke, but on a vit’s swingarm the extra material rises much higher)