In my use case and preference, the FM909 has a pretty steep seat tube angle for XC racing. I've got an FM936 and absolutely love it as an all-arounder. But most of my XC races are fairly low elevation and aren't very gnarly. The race I care about is smooth enough that I don't run a dropper, it's about 32 miles and 1800 ft ascent, lots of two-track, smooth singletrack, etc. For those types of races, I keep my LCFS911 around, the only downside in my opinion compared to other name brand frames is weight, it's about 2100g in large (without shock), compared to 1300-1600g for the high end name brand frames out there. When riding my FM936 hard on flat ground, I definitely feel like I'm right over the BB with a lot of weight on my hands, it's when I get into the steep stuff that the bike feels perfect. If your races have lots of steep climbs and/or are chunky, the FM909 is probably perfect.
Counterpoint, your Spur frame should be about 400-500g heavier than an FM909 frame. Is 1 lb enough to make a difference in your races? Do you have desire to keep the Spur as a 120/120mm downcountry bike with burlier tires while having the FM909 as a 100/100mm bike with XC race tires? As 25 lbs, I'm guessing the Spur is already built up as light as possible, what do you really think you'd gain by building up an FM909? Do the shock/fork on the Spur have ability to convert to lockouts?
