How do I find the breed of my dog (dog experts welcome)?

Ok, the pound said she was a border collie boxer mix, but I think she's part greyhound or something. She has shiny short black hair. There is a white stripe on her forehead/muzzle that goes down and ends on her chest, just like a border collie. Her paws are white partially, like only white up to just past the toe bones. When you look at her jowls, or mouth from below when she's panting, you can see the boxer part. But there's somethings different about her. I swear, when she wags her tail, it feels whip-like because she is really strong. Whenever she runs, i think she uses the double suspension gallop, some method greyhounds use to run. She's a fast runner. But I don't know if she is a greyhound or something else like a whippet or an italian greyhound. So I measured her and she's about 25 inches from the ground to her back and about a yard long. So, what do you think? Oh yeah, also she's older now so now she has more white around her eyes, they look like eyebrows. She has more white around where her white stripe is. Her personality is goofy. She's sneaky though. She is very loving, though, except when she's tired, she wants to growl at everyone. She is persistant, and won't stop until she wins, just in case those personality traits correspond to any other type of dog. Sorry this was so long. So yeah, please help me :)