From what I am reading now, it appears that the OVF uses compression level 5. It is possible to gain extra compression by using a tool like 7 zip but the gains are very minimal. On a 4GB VM you may see it drop to 3.9GB if you compress it again using 7zip. The minor gain isn't worth having to compress it twice IMO.
Well we pretty much know the size, if it runs in a VM on a Type 2, it's not big. And if we are just talking about some math, what's the purpose of production gear?
My dad used to do linear algebra for Eastman Kodak. He could use the mainframe when needed, but mostly they just bought him a high end laptop and let him take it home. Meant he could do his math modeling anywhere, anytime. Was much more flexible. Unless he had a rush job, no reason to tie up the mainframe.