Andrew, In my successful experience, cold calling and sending out letters are an outdated hard way of getting leads. For example - how many properties can you really see driving? Then skip tracing them then hoping the owner can actually entertain your idea of buying their home. I feel this is an outdated way of trying to get in front of motivated sellers. We are in the 21st century and a lot of digital marketing can be applied to easily make great use of your time. For example, I have a full time job, run a company on the side, and find my own deals as well and do flips. We all have the same 24 hours, its what we choose to do with it that makes the difference. In business its leveraging technology and your skill set to find unique ways to make your processes efficient, cheaper, faster, and to be able to scale it.
I pretty much wrote this for another person as well - I think if you focus on social media marketing and digital marketing it paves the way to getting better and faster results.