The hassle/cost of upgrading an '040 card may
actually exceed the expense of just buying
an '060 card to begin with. The '040 is 
a decent performer as far as the old machines
go.
But if you're going to do it anyway 

, 
an EC060 clocked at 75/80mhz probably 
would be similar during FPU intensive calcs 
as a full '040@40mhz. In all other areas your 
'060 would be noticeably faster though. 
(some programs (blizkick?) do require 
an MMU however)
BTW: oempcworld.com is selling 64mb FPM
SIMM's for $14.85...I paid about $20 for mine
(inc. shipping) and it works flawless in my
1260 card.