I never knew Iwasaki made anything above 6500K
Venture bulbs are most likely the cheapest ones out of the 4 listed. While I've never seen them personally, those who have them seem to like them. XM bulbs are nice and bright though. You need to be careful as there was supposedly a bad batch that came out a while ago that was prone to cracking
The XM 20000K is a blue bulb with very little par...that's what I've read so far anyway.