My 2007 Impreza wrx 2.5 is due a service. Last year I used 10w40, which I initially thought was quite thick but have had no issues with. My question is what do you guys recommend in terms of engine oil grade? The car is on 110 000 miles so the thicker oil may help it but I have seen people use 5w30 as well. 
Any help appreciated 

thanks

I always use 5w30 as that is what it specifies in the owner's handbook. Never had any issues. I change it every 5000 miles. Care now on 125k miles.

You can ask Opie oils for advice as they can give you the best option for your car and how you drive it/ any mods.