Can the increase of Information Store size affect backup length

I followed the procedure here -> http://support.microsoft.com/kb/912375 to increase the size of users mailbox stores from the default in SP2 to 65GB (Max 75). Would doing this increase the length of time a backup takes? The backup usually took less than 3 hours to complete, since increasing the mailbox store size its now all of a sudden taking much longer, more than 8 hours. I understand that this could be a coincidence but I have to other explanation at the moment.

1. Would the store size increase have anything to do with backup length?
2. Was my store size increase to 65GB overkill?
3. Can I safely drop the size of the store in the registry from 65 down to say 25 without any issues?

Thanks.