Amiga 2000 ram

[AmiDude]

This is the fastest ones I can find listed http://www.ebay.ca/itm/18PC-NEW-M5M44256AP-10-MITSUBISHI-256x4-100NS-DRAM-/131258440234?hash=item1e8f9cda2a:g:VAMAAOSwbqpT2~vY
They are 100ns
The rest all seem to be between 70 and 80ns

100ns is actually slower then 70ns. The lower it gets, the faster it is.
However, if you only want to use it on a RAM card, 100ns is fast enough.
60ns ~ 70ns is only better for accelerators cards.