Bill,
Got both working.
The advantage/attraction of the UNO is I have the GPS data-logging shield all ready to go - it has the SD card and the GPS module integrated in to the shield. And, I also have the data-logging program for the SD card.
I do have a shield kit for the mega and another SD card so maybe will go with that. However, it will only gain me a factor of 2 in my data rate.
Once again, much appreciation for your insights and suggestions!
Peter