As far as differences is ester weight, without actually calculating the mass of the enanthate & prop ester,
I beleieve the diffirences are that ca 20% of the test prop will be ester, and 30% of the enanthate.
400mg test prop is 320mg actual testosterone. Sustanon is a blend, but both test phenylpropionate, isocaproate and decaonate have from 30-39% ester weight.
So 750mg sust is ca 487mg actual test (when doing an approximation of 35% ester weight total)
Which would mean in theory that 750g sust should provide more bang than 400mg prop, but not that much.
Whether there are differences that come from the absorbtion pattern of test prop vs sust,
msam76 has a good point about water retention, since prop is so much faster both in and out,
it may cause less water rentention than the long actin tests.
Thats probably because with long actin test you eventually reach higher blood levels (most of the time),
than with the prop that will deliver more of a spike, and then let blood levels down again before next spike.