Folks, I have no opinion either way on the aftermarket 256 meg chip, but I do want to bring one thing to your attention if you are considering buying a 256 meg or larger chip:
The system software that Garmin provides to operate the GPSR is only tested with either the chips that Garmin provides (in the case of all the GPSR's that use the SP III form-factor chip), or with storage media that Garmin specifies as suitable for the device (in the case of the SP 26xx device).
So, if you use out of spec or non-supported media - such as a 256 meg chip in a SP III, or an out of spec mini hard-drive in a SP 26xx (out of spec meaning, it fits in the slot, but is not on the list of Garmin compatible media), then you are kind of 'on your own' if future releases of either the cartographic software or the system software don't work with the out of spec media.
By example, when the larger sizes of Garmin chips started to appear in 2001 (the 64 and 128 meg sizes), quite a few people bought them to use in older Garmin GPSR's, such as the original StreetPilot, which only support a chip size up to 32 megs. They were then quite disappointed to find that although they could load 128 megs on the chip, either the GPSR would not address more than 32 megs, or if it addressed more than 32 megs, it could not cope with more than a certain number of map segments on the chip (a number that was large enough for 32 meg chips, but too small for 128 meg chips).
Considering all this, I think it would probably be a safer course of action to purchase a second 128 meg chip, rather than get a 256 meg chip and sell your original 128 meg one. At least that way, you can be sure that you won't have compatibility problems down the road.
Having said that, though - it is pretty clear that the "writing is on the wall" for GPSR's that have limited storage capacity, such as the GPS V at 21 megs, or the SP III at 128 megs per chip. Everyone saw what happened to the map sizes (and the map segment sizes) with the version 6 release of CN and CS Europe - they took a big jump. No doubt a similar big jump - following a logarithmic growth pattern - will take place with the version 7 releases in 2005. Remember that the vast majority of automobile navigation systems run directly off the CD, not from storage media that CD data has been transferred to.
This whole 'data growth' process is no different than what happened with computer application software sizes throughout the 80's and 90's - data will expand to fill the storage capacity available for it. I still have a single-side, low density 480 kb floppy disk that not only contains the complete Microsoft Word 1.05 application, but also has space reserved on it to store the documents you were expected to create. Now, the same program - presently at version 10 - comes on two CD's, and the total size of all the files associated with this application is well over a gigabyte.
Buying a new SP III today (and planning to use it for 2 or 3 years) would only be a wise choice for a person who does not plan to travel very far (e.g. more than a 100 mile radius) from their home base, and does not want or need any navigation capabilities beyond what the SP III currently provides. If you want to run with the big dogs and stay current with both cartographic software and operating system software capabilities (road preferences, custom avoids, proximity warnings, etc.) for the next 2 or 3 years, then you really should buy the most 'current' product - in this case, the SP 26xx. Buying a new SP III to keep capital costs low, then planning to buy a 256 meg chip to increase performance is a bit like a teenager buying a BMW 3 series with a 1.6 litre engine, then planning to put a 4 barrel carb and fancy exhaust on it to boost performance. He's never going to be able to keep up with the 540's, much as he may dream of doing so.
The picture is not as bleak as it sounds, though... the street price of a SP 2610, today, is lower than the street price of a SP III when it was first introduced in 2001. Again, it's same path as computers have taken.
PanEuropean