Keep in mind that you'll have to convince the IO - since you'll be entering as a visitor - that you will be going back to your home country at the end of your visit. The more reasons you have to stay (such as, for instance, the fact that you're entering with your girlfriend and planning to apply for residence

), the stronger ties to your country you'll have to prove (return ticket, job, school, lease, etc.). If you don't have those, I wouldn't recommend mentioning PR application.