I’ve run both Shimano and Sram–even mixed and matched the two in the same drivetain on the same bike. Both work well. I’ve had both XT and XTR along with Sram X9. Unless you have no money concerns and are a gram-counting xc racer, I wouldn’t go "all out." There is a huge price increase for very little wight savings and possibly even a durability penalty. I had a XTR rear derailleur as stock on the last bike I bought and within a couple months, broke the carbon fiber cage on it. I replaced it with an XT which has performed just as well for half the cost. I suspect there would be a similar relationship between the two Sram components at the top of their respective lines.