I think I've gone on record before in saying having experienced a Garmin V and now a SPIII, I'd happily forego the advantages bigger, colour screen of my SPIII for data card capabilities in my old Garmin V.
My SPIII is lovely in the car the big unit, nice clear colour screen and the voice prompting all very nice sitting there on its bean-bag mount (the Mrs loves it), the same on a bike isthough IMHO overkill, by that token then I'd give the samller unit a go and decide if I can live with the smaller mono unit and lack of memory capability. Secondhand Streetpilot Colormaps are cheap and ten-a-penny as they say - GO FIGURE.
If Garmin ever brought out a Garmin V with data card I'd be very tempted myself.
Also don't overlook the Etrex options, Howard and Ian could fill you in on them, sorry to introduce a new unknown - but better to consider all the options first, but they might be just the ticket. Paul G could tell you about the Garmin 176 too, another as yet unconsidered here.
If you're in no rush then consider Dutchman's GPS weekend up in Edinburgh as you will probably get to see, play and talk to owners of all of them - if you can't manage that then he has put loads of useful GPS links on the BMW Scottish Section Web Site.
You've probably worked out in all this that my main criteria is the autorouting capabilites of both the V and the SPIII, hence I can't give much of an insight into the non-autorouting models.
