OK, so I tried to test it in practice, starting from 120 MB down to 25 MB. The largest that went through had 35 MB; the larger ones bounced with:
> Remote Server returned '552-5.2.3 Your message exceeded Google's message size limits. Please visit 552-5.2.3 https://support.google.com/mail/?p=MaxSizeError to view our size 552 5.2.3 guidelines.