Yeah, generally my approach has been to look for the fan with the higher rated airflow and less noise, a lot of times the parts they're cooling already run warm and prolonged heat will eventually make them fail, so in the interest of having stuff stick around, I try to do at least as good of a job moving air as the OEM fans.
I don't know about Siglents, but ... as I pointed out in the "Rigol fan replacement" thread, a Rigol is designed to work in 50 degree Celsius ambient temperatures. I imagine Siglents aren't much different.
That means there's quite a lot of wiggle room if you're using it in a 25 degree office.
Sure, but the wiggle room is a benefit for test equipment. Their overall lifetime is higher because of that sort of tolerance, and since I do occasionally upgrade my kit and sell them, I don't want to put in some dramatically quieter but just barely performing fan that will just be a timebomb in any space that isn't an air conditioned office. I also end up getting used equipment pretty commonly, so to try to get a nice long lifetime out of a piece of gear that may have already been heavily used, getting a closely rated fan is a precaution I have no issue taking. I've used my scope and counter outdoors, I'll occasionally carry stuff to somewhere else, and if it's possible (and it usually is), I'd like for them to perform well in any situation they normally would even if I modify them.
Sure, it's gilding the lily, as Dave would say, but so is input protection and extra EMI filtering on the power cable..... it may not be required for normal operation, but it sure comes in handy sometimes!