I seem to hit a limit around 250 items, however, the quantity does vary as I try to add more. I need to increase this to 375. I switched to a radio button and I was up to around 300. I also read that tables do not like capitals so converted to lower case with little impact. I have tried explorer, firefox and safari on a PC and MAC with no impact.
I did look at the class-bp-xprofile-field-type-selectbox.php file and did not see a limiting parameter. The posts you referenced said they had over 1,000 items so I am not sure if it may be something with my host. Anyway, below is my theme and plug-ins, any help would be appreciated.