>Mouser has FOX500-20 HC49U 50 Mhz parallel mode xtals, but I
don't specifically know if they work with SX.
>Digikey shows Citizen xtals at 50 in the latest catalog, they
don't appear to be 3rd overtone.

Anyone tried them up already? Thanks for checking up Dan.

>I have a Scenix SX28-52 Demo Board, and the xtals there are
labelled: ABRACON 50.000M-F AB 9703. Never heard of Abracon.

Contacted them (http://www.abracon.com), they were helpful and fast to
reply so far.  I guess their's must work ???  Is it alright to pass
email addresses?  I did so earlier.  Better not to this time.

>Also, I've been using Epson SG-531PH oscillators (not cheap,
from Digikey) on my own boards. Been running the SX at 60 Mhz
this way.

It would be good if it can fit into HC49U footprint.  Overclock an
already speedy SX, brilliant ! What's limit you've pushed?  Put a fan
in and see how fast it can go.  I can send a 486 cpu type of fan from
here (Singapore) if you want to try?

Cheers, Ling