Hi there, I do a lot of SL photography and have a lot of experience when it comes to profile pictures.
Standard: (not edited)
Portrait: 450
Mid: 650
Full: 850
COUPLES: 1,000
Artistic: (edited)
Portrait: 1,000
Mid: 1,450
Full: 1,800
COUPLES: 3,000
Here is a few examples (artistic and standard)
I have more on my flickr if you're interested. https://www.flickr.com/people/heartlesslittlered/
Feel free to drop me a notecard inworld @Heartlesslittlered or on my flickr if interested.
Have a nice day!