Rod Petersen passed along the following information today:

1) Atari currently keeps about 100,000 27512's on order with AMD, our primary
   supplier. 
2) Leadtimes are at 18 weeks so this is necessary. 
3) Despite the requirement for 200 nS parts, all they can get is 250 nS access
   time parts. ENGINEERS BEWARE.
4) AMD says that the 250 nS parts are screened to run at 170 nS at ROOM Temp.
As a Result:
1) Based on this, both Stempler (system II) and Snyder (XYBOTS) have issued
   deviations to use 250 nS parts in place of the specified 200 nS parts.
   Typically, they have found a worst case access time requirement of about
   220 nS which allows slower parts to run OK at temperatures less than 70
   degrees centigrade. 
2) If you can squeeze out a few nanoseconds either with chipselects always "on"
   (with consequent increased power consumption, oh well) or with faster
   parts in the glue logic, it may be worth the trouble if it allows you to
   specify 250 nS 27512 EPROMS. That way you avoid the judgement call later
   in production when 200 nS parts are not available.