[allan87]

but it says a lot about where the bottleneck lies; the sdcard memory technology so anything that can speed this up without breaking any stability is more than welcome IMHO

My own experience with a class 10 card v. USB was different. I could not discern any difference in the speed of the interface between the two (navigating was very acceptable in both).

In terms of performance, I suspect that the issue pertains more to differences from one SD card to another rather than generic differences between SD cards and USB sticks:
- there is a well known issue of Raspberry Pi being fussy about which SD card one uses, regardless of class or size;
- many people have reported significant performance improvements when moving to USB;
- others have not seen performance improvements. I recall seeing benchmarks posted elsewhere with a particular SD card and USB drive having virtually identical read and write times.

What this suggests is that you have to be a bit lucky with your SD card, whereas most USB sticks are OK. Personally, I use an old, slow 128 MB SD card for 'flash' and a USB stick for 'storage'. My reason was to avoid corruption of the storage volume (particularly while using alpha builds). Two good reasons to use USB, I think.