Loading maps onto Oregon 300

[Matthew 7:7 Too]

Hi all,

I'm considering replacing my eTrex Vista/TOPO GBv2 with an Oregon 300. But the TOPO maps are too big to load all of GB onto the internal memory in one go. (I have them loaded onto an SD card in the eTrex. But if I do this, I can't also plug in a GB Discoverer SD card! (I'm looking to buy the forthcoming GB Discoverer Northern England & Midlands when it gets to the shops.)

I could load part of the TOPO GB maps on the internal memory, and then change regions when I need to, or copy the TOPO maps and GB Discoverer maps onto a 4GB SD card. And what it I then want to use the TOPO maps with a different GB Discoverer map??

Any advice please on the best way to use both TOPO GB and the GB Discoverer maps on an Oregon 300? (I had thought the solution was to plug the GB Discoverer maps into an Oregon 400t, but understand that its TOPO Europe maps are even less detailed in the UK than the TOPO GB ones are!!)

Chris