ya lor, at least if write speed exceed 6mb/s quite acceptable la.. in my XZU i'm also using the sandisk ultra, but this i bout to use on my DAP, because its cheaper.. but then...
yes, ultra is red/grey color, my 32gb in my XZU is that color, speed is similar as yours.. but this black color i bought just now, printed on it is "class 10" but write speed is wayy lower
no, i just put it in my XZU and format from there, then do the test
yup, sandisk ultra is red/grey color, my 32gb is also that color.. i bought this one because its cheap, want to use to store music files for my portable player
oh really? this one printed "class 10" means its a clone/fake??

hmm maybe its only class 4 only..