Is this a need or want scenario...I'm asking because I'm in the same boat, with me it's a want more than need. If the new 7D has 24 MP, I'll buy it as an adjunct, otherwise wait on the big MP one...if I live that long.
I fail to understand why anyone who is not a professional would even own a printer...it is not cost effective. What are ya gonna do with a plethora of prints...ya only have so much wall space...shoe box in the closet like your grandmother did? There are a myriad of on-line printing companies that usually cough out better results, at a far cheaper price in the long term, than you could hope for.
I doesn't take a genius to use the ruler method if you're adept at Photoshop focus stacking. Simply take a series of images at incremented adjustments>import them into PS as layers and stack them...the masks will tell you where you ought to be.