I have NOT (as DP prophesied) have my coffee yet but I will attempt to assist here, Matt.
DP pricing seems good. I'd go with that. At the top of my game in graphic design I was pulling in around $80 per hour. So $55~$65 is a good middle ground.
I don't like flat rates too much, but clients love flat rates as they know what they are gonna get billed BEFORE you do the work. Don't blame them.
So, I always worked based on my hourly rate... but a lot of the time it was transparent to the client. In other words, I'd make sure I had a very good and clear talk with them at the beginning and really figure out what they want. Then I'd go away and estimate the time (this gets easier as you do more work) it will take, I'd add 10 ~15% on top of that for "surprises", and then figure out a "flat" rate based on that. Then it was up to me to keep things ON BUDGET.
The last few years of my graphics career I could pretty much nail anything from a $200 project to a $3600 gig and not need to "adjust" costs at the end. This was from knowing my own abilities well, and understanding how to read a client accurately. (fussy clients take more time and you need to compensate yourself for their fussiness!
Again, I'll stress (and you may have done this already by the sounds of it) how important it is to know EXACTLY what the client expects of you. Equally important is your own Self-Knowledge of how fast you work and how well you know your stuff. That, coupled with a good hourly rate (you'll need to find out what the locals are charging to make sure you are competitive) means quoting becomes a breeze and no one works in a crappy resentful nasty energy of despair and gloom!
*edit* And also, as I was overlapping my graphic design with digital image design and photography, I had two rates going. My $75~80 rate for graphics, and at the time around $150 /hr for photography and creative chopping work. I actually had two columns in my invoices / quotes at two different rates. Some cities/towns won't support this double standard, but Vancouver area does. Now, since I've hung up my "graphic designer" hat I'm based in around $225~$250 an hour for my photo art work projects.
My point here is - different work has different value in different towns... but I'd say watch out for TOO LOW rates for "GRAPHIC" work when, in a PHOTOSHOP / DIGITAL IMAGE situation, you may be worth a good chunk more as far as your talent goes. Lots of people know how to put words on pictures out there - not so many know how to CHANGE the PICTURES and do it well. That is a different skill set!