Need help with SDHC card selection

Dear community,

Please help me to choose SDHC card for my Beagleboard C4.

I think, that 4Gb will be enough for me. But the question is read/
write speed: is it necessary to buy expensive class 10 SDHC card (i.e.
SanDisc Extreme III with speed of 30 MB/s and $40) to get good
perfomance for Ubuntu/Andriod or not?

Does BB really support 30MB/s or it is beter for me to buy cheaper
SDHC card (i.e. Transcend SDHC 4Gb Class10 for $12) and spent a
difference in money for something more usefull?

Thank you for support,
Alexander Yerezeyev