I have one IM6 (now WT), two LT's and two BIIx's, and they are all great rods. I would not consider any of them fast in any way. The BIIx's have stiffer butts, but they are noodles in the upper mid and tip sections, the LT's are amazing rods in the shorter lengths, but tend to have negative tip action as they approach 9 feet, and my 9' 5wt IM6 is simply an amazing fishing/casting rod with great fishing mojo, but it is heavy and slow.
In comparing WT and LT actions, I would consider WT's to be full flex rods, and LT's as mid flex action rods as described by the
Orvis Fly Rod Flex Index. I would also consider BIIx's as Mid Flex, but at the higher end of the spectrum, when compared to the LT action.
If I were going to buy another Winston rod, I would only consider either a WT or LT, since they are truly Winston's bread and butter action rods. In my opinion, all BII's are outside of the Winston realm, and frankly, there are better rods with similar action from other manufacturers.