Depends on what you want to play. Star Wars, Geograph Seal, Super Street Fighter 2, Mahou Daisakusen are pretty much unplayable at 10mhz imo. But all are solid games at 16.
24khz would make Geograph and Mahou even better, but they run well enough at 16 for my tastes. Mahou really requires an 030 if you want to play with full-animation turned on.
A lot of games are simply smoother on 16 over 10. Play Thunder Blade at 16, and you will never want to play it at 10 again.
There are also other benefits to 16. Nemesis '90 Kai will use a more advanced sound driver if you are running at 16mhz and have 4mbs of RAM. The driver allows more software mixing to simulate more sound channels. At 10, it loads a simpler driver.
Out of the box, Dragon Spirit only runs at 10, but there was a fanpatch to make it run at 16. The 3D patch actually includes this already, and it really needs the 16mhz. Stage 3 at 10 gets some jerky motions which break the sync with the glasses, killing the effect for a second or so, but run it at 16, and it's a lot more playable.
Overall, if you are used to having 16mhz, you won't want to go back. But if you only have 10, you can still play most games and have a great time.
These days, since most people are paying a LOT of money to import these from Japan, I think most people are willing to spend a bit more and get a later unit. The XVI is overall the best single unit to own. It's the right performance for what it costs to acquire. SCSI>>>>>SASI, and if you are going to spend $500 to import a Super, you may as well go all in and go for the XVI.