There are literally a 100 or more bikes you’d be stoked to have as your new ride. The technology, suspension and refined nature of the parts hanging off the frames these days is nothing short of amazing. I work in the cycling industry and ride a lot of bikes(both medium and high end mtb’s) and am stunned with how well so many different bike models and brands ride! First and foremost the bike needs to fit you well, this would be my top priority. As for demo’s, go to the various brand websites and facebook pages. There you’ll find information on upcoming demos. You’re likely looking at Spring before you find one to participate in though. Some brands partner with their dealers for test rides, while others are active in regional demo events where lots of brands demo all at once.
Sounds like you like the 29er platform and based on your other comments its a good fit for your local riding scene and style. 29ers are having a bit of resurgence in that they are being built to handle a wide range of terrain(shorter chainstays, slacker head angles, longer toptubes, longer travel, etc) and riding styles. This is not an endorsement or recommendation, but personally I’m having a blast on the 27.5+ platform. Ton’s of traction both up and downhill with the ability to run insanely low tire pressure makes a 135mm travel frame feel bottomless when set up correctly. Yes, they wheels and tires are a bit more sluggish than a narrower or smaller profile 29er but the fun factor goes up exponentially for my riding style and local terrain(live in Reno, NV and ride Lake Tahoe/Downieville trail systems with big climbs and big descents). I agree that the $3-4k MSRP price point is the sweet spot for the best frames with decent enough components to enjoy the trail(think carbon frame with SRAM GX or Shimano SLX)
I’d recommend combing Craigslist ads for a certain radius(say 200 miles around your home) and look for new or near new bikes. This way you can physically inspect and ride the bike you’re potentially going to buy beforehand. I’m always in the market to buy or sell bikes/frames and see some very good deals on high quality bikes that are new or nearly new for a fraction of the original MSRP. Pinkbike and MTBR classifieds are also good resources. People get hurt, have good intentions of riding, buy the wrong size, etc this can always lead to good deals on new equipment. Dealers also post on Craigslist trying to unload previous year models which are usually the same or very similar to the current year. You could always buy that SC Hightower with the SRAM GX build and upgrade as parts wear.
Don’t over analyze and don’t second guess your purchase once completed, just ride and enjoy this fantastic sport!
Cheers!