Most usb sticks are for cheap small memory transport, not performance, not least because they are easy to lose or have stolen so a £40 16gb usb stick will barely sell but a £10 32gb stick will sell by the bucket loads.
USB 3 is very useful, though mostly because USB 2.0 sucks, esata was always brilliant long before usb 3 was available, I think its still much better for random performance, but a massive step over usb 2.
Fact is with nand flash you can get just about any read speed you want, write speed is harder to deal with but read speed is purely raid 0 across as many chips as you want, nothing more complicated than that but cost increases as you've got more chips, more traces and you need a more complex(expensive) controller to deal with all the channels.
Even a basic 2.5" external drive usb 2 will limit you to sub 30mb/s, usb 3 will get 80-90mb's on a cheap hard drive. Stick an ssd or a decent memory stick and usb 3 will fly, the cost of memory sticks really isn't worth it for anything but size. You can get a 128gb ssd, stick it in an external box and get ridiculous speeds.
99% of usb sticks are cheap, single/dual channel controller, and cheap slow memory meaning you'll get 5mb/s read/writes on any interface.
Personally I'd prefer to spend The £80 on a 128gb ssd, a £5 enclosure, either esata or usb 3 and blow away a super fast memory stick on price/GB, performance, everything.
