Hi RubyTuesdays,
Sorry no one has replied to you yet, and sorry to hear you are in this situation, unfortunately one a lot of us can relate to. I ended up having success on my 7th ET with fresh embies at day 5, but I have heard/read of plenty of successes for others on day 3 or day frozen embies, so there is every chance.

From what I understand with regards to your embies arresting around day 4, it is the male DNA that kicks in after day 3 and is responsible for getting them further, however assuming you have had your DH checked for these issues. Otherwise if you are using donor eggs you might be in the same position.

I guess you need to make up your mind which way you feel more hopeful for, if doing a donor cycle will make you feel more confident in your chances, then go for it.

Wishing you all the luck with what ever you decide. xx