There was only one ROM upgrade A01 R74809 (010504 or Jan 5, 2004) and they pulled it. I flashed R74809 over A00 on my original x3i and pOutlook worked faster on A01. R71183 and R75705 are just patches. They have been shipping x3i's with A01 - just went through 3 of them.
Yes, you cannot flash with an older or same version. I do not have any problems with wifi connection to my SMC2804 802.11g router in mixed B+G mode with SSID disabled, firewall enabled and WEP enabled.
However I did have a big problem with defective short range wifi on x3i's. However I don't have faith in Dell x3i's now.
10 digit vs. 6 digit