Let me guess.... the person at your LHS is a 16 year old dork who doesn't know squat about airplanes or engines isn't he? I say that because that's what works at one of the LHS's around here and they say the same sorts of stupid things. The really absurd part is the 50 degree figure. Even in my relatively moderate area that would eliminate a lot of flying time if it were true. The people who build engines make them to work as best possible in the varied conditions in which people actually fly.

When the weather cools off, go a few clicks richer and fly. Extreme cold climates may require a little more effort to start a cold engine but there are plenty of people who do that successfully all the time.

In fact the cool, dense air is great to fly in.