I purchased my car at Grand Subaru and wouldnt go anywhere else for warranty work (performance i go elsewhere). They worked on my car all the while knowing I was stage 2 without any questions and even allowed me a courtesy car for over a week. Great guys over there. John (service manager) is a great guy to deal with and very honest.
Ive been to Gerald also but had a poor experience in every way except with Sandy in sales who recently just transfered to Grand (awesome!)
On the oil thing, i use Shaeffers and change mine every 2-3k because I'm anal about it and it helps me sleep at night. This is regardless of temperature. That being said its personal preference. And while the temperature can have an impact on wear, i really doubt it would/should change your intervals that drastically. If at all. If its a quality oil and you feel your engine still runs smooth and feels good then stick with your current schedule.
Hope this helps!