Maybe you need to go back to the Treo? Sounds like you won't be happy with the BB.
Have you looked into BES or a hosted BES solution? That might provide what you are looking for.
If I remember correctly from my Treo days, the quickest I could get my email was 15 minutes. BIS is true push email, in that email is pushed to you about every 15 minutes, sometime faster. I don't have to go out and ask for it.
I find BIS to be very efficient and it works well for me. I do not see the need for instant, near real time email access.