You know, what you're post indicates, you're pretty much where I would think you should be in terms of durability. 6 - 8 hours should be around 15 sets? That really isn't bad for 17 gauge.
I would recommend the following:
- Start using string savers religously, they really do help if you install them after every match. Any place you see some fraying, just slip one in. After you get home from playing, check for notching and put one there too. If you know where you start fraying to begin with you can put some in before you even play with a stringbed.
- up your gauge to 16, that also will enhance your play time and you won't see a big difference in your play. pacific gut is gauged thin IMO anyway
I don't know that tough will necessarily increase your string's life. Some folks have reported longer life, but I haven't played enough with Tough Gut lately to offer an informed opinion. I know that Prime seemed to play a bit longer than Classic, but I didn't track it really too closely.