I think you are in a perfect position to start the 18/55 then.  The program puts in the miles and they increase rather quickly.  You will also have some hard workouts.  If your base was not yet at the minimum, your risk for injury may be too high. 

I would follow it and take the first couple weeks as prescribed and enjoy the "easier" weeks if that is how it feels. If you need to, add a couple miles here or there or do an extra recovery run on one of your off days. You won't want to push it too much though as it is a pretty aggressive schedule - expecially the first time around.

Be sure to get Pfitz's book and read how he suggests you run your various workouts.

Good luck - I had great success with that program 2x and am now starting the 18/70.

I have used the Pfitz program with modifications, although not your exact question.  My guess is that you are running 5 days a week for that mileage.  If you note the Pfitz plan only starts you with four days a week for the first 3 weeks or so (I don't have it in front of me).  Pretty easy to just keep running the extra day to me.

As the mileage builds you may want to "back off" to the scheduled mileage or you may find that you keep being a little ahead of plan. No problem with running a 18/60 plan, or whatever if you want.

Southern Man

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We're on a road to nowhere.  Come on along.

What's the name of the Pfitz book you recommend? I am having a hard time finding it at the book stores. Thanks!

I believe I got a copy on Ebay for about $4.

Will your starting mileage be anywhere near the stating mileage of the 70 plan? Remember the first mesocycle of the Pfitz plan is "base training". I think many people don't take that into consideration. If your mileage is going to be near the starting mileage of the 18/70 plan(53 MPW I believe) and your long run is near the first long run of the plan(13 miles?)than I say go for that plan. Build your current base training around his format...that is 1 medium long run, 1 long run, 1 day of striders(altered with a couple easy tempo days) couped together by recovery jogs. Than picking up on his schedule will not be of anything different. I see no reason to seperate your base building from the first mesocycle of his plan. If anything just add on to that mesocycle.

The thing I really like about Pfitz is how systematic his training is. Each cycle prepares you for the next cycle slowing adding in the proceeding elements. Study the trend and just extend the base to your current training.

If you have the book and you should compare and contrast the 55 and 70 plans.  They are very close in layout.  So with a bit of imagination you can create a 60 or a 65 plan that lies somewhere in between the one in the book.