memory size

I have a question,I have read almost every post and no luck but I may have missed it,what is the largest memory card I can use in the 610i and will non-sony memory sticks work,I ask this because when I had my Motorola Rizr they said to only use sandisk up till motorola had their own brand and nokia said to use only nokia branded memory,which I really think is BULL but they are not a high end phone like the SE which might make a difference.
Also I was wondering is the 610i a higher end phone than the 810i even though they seem the same almost,except that the 610i has A2DP bluetooth?I do not understand how their numbering system works as to how to tell which is the higher end phone of any of the phones they make?  You could tell motorola and nokia just by how cheaply thay were made but that is not the case with SE phones,none of them even come close to looking cheap!!!!