Whencomparing the bikes (both sized medium, factory builds), the first figures will always be the 27.5 bike vs the second as, obviously the 29er (unless noted). First though, some stats/details of what is being compared. I rode the same location on the same day (Sunday), 2 weeks apart, with similar TSS for the week leading into each ride.
275 will accelerate faster and is more responsive. The 29er will maintain speed better and track straight line better but harder to accelerate. The scout 275 can take up to a 2.8 wide tire which kinda closes the gap in wheel size and will take a lot of the edge of riding a hard tail. So that choice is yours. Acombination between a 26er and a 29er, a 69er has a 29” wheel up front and a 26” wheel down the back. A small amount of weight is saved and they accelerate a bit faster than full 29 inch mountain bikes but the big difference is with the chainstay. A shorter chainstay brings the rear wheel in close to the bottom bracket. 275 is more playful and maneuverable, while 29 is faster and better at going over obstacles. What is more fun for you, being playful and maneuvering, or going fast and cVEl.