Can't speak to the yeti. I did have a scalpel for a good few years and it is a stand out bike. I did no hardcore racing at all, just general MTBing. I now have a rush – enjoyed the scalpel miles more.
The scalpel is an exceptional design – a brilliant bike that stands out. The rush is just another short travel XC bike – good, but really no better or worse than every other one on the market. So there's something to be said for riding a great bike – it used to put a spring in my pedal stroke 🙂
The only thing to maybe be wary of is the scalpel does have a bit of a head-down, racing fury type of geometry. I found it fine comfort wise – you could ride it all day, but it could be a real handful on technical stuff compared to a modern all mountain set up. I'd need to be restrained putting it through rocky step downs and the like – it would take a skilled rider to really blast a scalpel through technical sections IMO. No idea how the yeti compares.
ETA: Sry for the biased opinion!
