Question Managing large volumes of SMS

Hey guys, I was hoping you might be able to help me with a problem I've been having.

I have an HTC One, stock rom with custom launcher/home screen.etc, and I am trying to manage a very large volume of sms (50,000+).

When I first got this phone, I never told it to delete old messages as I liked to create backups. However, now the phone is just too bogged down as a result of all these messages.

I would like to have the phone start deleting messages once they get above a certain number. So to do this, I created a backup of all the SMS messages using the HTC stock messaging app as well as the SMS backup+ app. I then deleted all the messages, and used the stock SMS restore feature with the "delete old messages" option selected under the settings.

The problem is this thing has been running for 6 hours now, and I am not sure it is getting anywhere. How would you guys handle this situation?

Thanks for your help!