Lots of questions which I will do my best to answer!

The orange variant to which you refer is the I5801. It is essentially the same handset ( hardware is identical) but the firmware is orange- branded ( logos/ extra apps and other pointless crap). The handset is also locked to only accept orange UK sim cards.
The reason froyo was issued to orange handsets is that orange spat their dummy out and rushed froyo through to keep their customers happy. Their version has a few issues atm.
Kies checks Samsung servers based on imei/product codes and firmware version. If an upgrade is offered it will be loaded. If not there are ways to fool Kies into upgrading to a different variant firmware but this is very dangerous as it loads a new bootloader which can crash and kill the handset.
I can help load whichever version you need,- just let me know.