Ratings of 3/60 vs 3/80

[PPMcMahon]

We currently have a 3/50 and a 3/60, running various software packages.  I
am thinking of changing the 3/50 to a 3/80, because the 3/50 is very, very
slow. (The 3/60 is only very slow :-). Is the 3/80 any better - both it
and the 3/60 are rated at 3 Mips, I think, but is the newer machine any
better, quicker ... 

Will our existing third party software still run on the 3/80 (it had
better!!).  I know a Sparc would be great but all our software has to run
on the new machine.

Thanks for any information

Peter Mc Mahon
ppmcmahon at cs.tcd.ie