Is there a large difference between PPS and PPLNS? Sometimes I may mine for 16 hours a day or less, but definitely more than 12.

I have decided to make use of the low temperatures in my area and run my computer 24/7 for some days, which may be 10 or more. Here are the specs:
- i7 3770K @ 3.5GHz
- 8GB DDR3 1600MHz
- PNY GTX 670 2GB

I'm currently mining Litecoins, and the 670 is giving 190KH/s with scrypt while staying at 53 C and 80% fan speed(set manually), and using around 150W. I have a few questions:
- Will the fan survive staying at 80% all the time? I'm talking about a timeframe of at least 10 days in a row. I believe the temperature is in the safe limits for constant usage. I don't really know much about GPU limits, so any info is appreciated. I decided to speed up the fan rather than keep the card in 80 C.
- Will it stay profitable with the difficulty increases? Or is it better to mine another *coin and trade for BTC / LTC?