Also, does having the BB on a wi-fi network slow down BB push email?
WiFi makes no difference in delivery of push e-mail to your device. Chances are that your roadrunner e-mail account is setup under POP3 rather than IMAP. Accounts setup via IMAP (like Gmail) give you near instant delivery of your e-mails to your device. When an e-mail is setup via POP3 it does not provision for instant e-mail delivery. The BIS server will poll your e-mail inbox every 10-15 minutes to see if there is new e-mail. If there is, it will automatically push it to your device.
This is how it works for Outlook Web Access accounts (which I assume are similar to Roadrunner e-mail accounts). On my OWA e-mail setup, I get messages about 10 minutes after they hit my inbox. Not ideal, but it gets the job done...