How much better is BAT VK-3ix than the VK-3i?

Looking at these to preamps used here on AudioGon. Anyone done direct comparisons of the two? The VK-3i is older and usually sells for much less than the VK-3ix, but how much better is it in real world terms? I can't imagine that it is a night and day difference, and it seems that we always get caught up in the argument that because something is newer and updated that it is better. Maybe it is, but....maybe not. If the VK-3i is not that much better than the VK-3ix, why not buy the VK-3i and save the cash. I searched the archives for direct comparisons, but not much useful info.

This will get paired with a VK-55 amp, which I already have. I am also considering a VK-5i or possibly a VK-31 if I can snag one at a good price.

For now I am set on a BAT/BAT pre/power combo.
The 5i is a big step up from the 3i. I had a 5i and paired it with the VK55 for a few months. I loved this combo. I have never heard the 3ix but Stereophile did a review of the 3ix and 55 amp and loved the combo. Go to Stereophile and search. The 5i falls between the 3i and 3ix if you want to save a few bucks and the 5i lets you do some tube rolling :)
Thanks for your response. One thing that conerns meabout tube rolling in the 5i is that there are 8 6922's. With NOS tubes that can get very expensive considering you may not even like the sound of a particular NOS set of tubes that just cost you anywhere from $400-800 for two quads. Is there a current production tube you liked in the 5i? Another concern I have with the 5i is heat. My rack is open on all sides, but only about 10" from shelf to shelf, so it will probably heat up the shelf above it quite a bit.
I used Matsushita 6DJ8's in my 5i with good results. Do a search here and you will find they are good tubes and priced reasonably. I still have 4 of them. A friend of mine is using 4 of them to see if he likes them in his Audio Research preamp. I found them to sound better than the stock Sovteks thats for sure. The 5881's I recommend are Tung Sol. If you decide to buy a 5i change out the 5881's 1st and then proceed from there.

As far as heat, I ended up moving my 5i to the 2nd shelf and never had any heat issues or excessive heat on the shelf above. I think the distance was about the same as yours or maybe a tad taller.
I would go for vk-31 at $2100 currently for sale at agon. I think it is an excellent price.
I had been thinking of getting vk-3i/3ix/30 for a while, and ended up with vk-30. I wish I could pull out more $$$ to get vk-31, but I thought that my vk-200 would not be able to tell much difference between 30 and 31. My sources are not balanced, so I preferred vk-30 to vk-5i.
I see 3i < 30 < 3ix,5i < 31 in their price.
Your VK200 would be able to tell the difference in the 30/31 I am sure. Any changes when I had mine were noticeable. Ihcho does bring up a good point, the VK5i is xlr only unless you have adaptors.