Yes it is a MediaGX chip, and yes you could drop in a 300MhzGX but you have to remember that the motherboards FSB only operates at up to 33Mhz(indicated in motherboard manual)... By the way I am a overclocker by nature (PCs mostly) but this recent websurfer stuff has been rather interesting.
By the way, here is some background information about the Cyrix MediaGX processors: (Really hard to find if you want to get a 266Mhz MediaGX)
Developer Cyrix Corporation
Number of transistors 2,400,000
Register width 32 bits
Data bus width 32 bits
Cache bus width None
Address bus width 32 bits
Addressable memory 4 gigabytes
Floating point unit Integral
Primary cache size 16K
Secondary cache size None
Multiple processor support None
Clock speed (MHz): 120 133 150 233
Date introduced: 1996 1997 1997 1998
Operating voltage: 3.3 3.3 3.3 3.3
Design rules (micron): 0.6 0.5 0.5
I got the FSB speed from the motherboard manual however I have been looking around for other indications of FSB speed on various websites that have information about the MediaGX and found one to list the FSB's as 60Mhz and 66Mhz. This could be since in the manual the motherboard is mentioning Bus Clock, this could always be multiplied by 2x therefore coming up with 60Mhz and 66Mhz. Now, the 300Mhz MediaGX is operating at 66Mhz FSB and since the voltage selection goes up to 3.3v, you could run a 300Mhz MediaGX (renamed to MediaPC some say), at 300Mhz just fine in this motherboard. Pop a little larger heatsink/fan on the 300Mhz processor and boom you have a CHEAP nice pc. =]
