Everybody has their own opinions. I have a GTI300 and live in Central (Syracuse) New York. So far I have changed my oil, filter, and differential oil at 122, 504, 1001, 2008, and 2949 miles. I use Mobil 1 full synthetic 10w-40 in the engine, and Mobil 1 75w-90 in the differential. I can't find the 10w-40 anymore in 5 quart jugs around here so next spring I'm changing over to a 15w-50 for the engine. Your manual shows a chart with engine oil viscosity vs temperature. You have several different options for your particular area. Get your oil based on the temperature range you ride in. Personally I prefer a full synthetic oil. Here again, let your conscious be your guide. I buy my oil in 5 quart jugs from Wallmart and it's not that much more than conventional oil. I run full synthetic in everything I own from lawnmowers to my vehicles.