They're both Eclipse, but "no dead space
"is new. I think it may be an updated design with a different plunger. The old ones have .07ml dead space. I'd choose those if 30g 1/ 2" works for you.
Dilution depends on the compound. HGH requires less than Tirz, as an example. But all things being equal, erring on the side of more is preferable to less.
You (usually) can't see the type of degradation caused by concentration being too high. With lower concentration by using more BAC, peptides will stay in better condition over a longer term.
The other factor for certain drugs, like GLPs, is the dose volume determines how quickly blood levels rise. A 2.4mg dose of sema in 0.1ml will be absorbed much more quickly than the pharma volume of 0.75ml and potentially worsen sides, or even induce hypoglycemia (low blood sugar). This is referred to as pharmacokinetics.