I was racing 2 years in BUK, then I changed a team. So my second experience was with Swift 2009. Now we are racing Swift 2010 Premium.
BUK 2007/2008 is the stiffest but slowest. On the other hand it is more stable than any other boat. But there is problem with the footrests on the front seats. They are too close unless you are 160cm high. The second (the end) is too remote as for 200cm person and it is not stiff. Also the edge under the gunwale is moulded so you have bruises and it limits you a little to lean out. There is sometimes not enough space for legs because of the bench columns.
Swift 2009 has biggest torsional flex. (the front left can be up while the right back is down..) The gunwale is thin. But on the other hand it allows you to lean out more without any bruises.
The flex complicates weight distribution in the boat, but nothing you can“t cope with. Swift 2009 is also less stable, but if you know it, there is no big problem. The drummer seat is very low, you can use to it as well.
Swift 2010 (Premium) is very close to the stiffness of BUK. Handholds are best. All footrests with drainage are also best I tried. The absence of most of the bench columns is great. Front seats have more space for legs (this is where I sit) The gunwale is thick as on BUK so you will have bruises again.
But the steerer floor works a little under your feet. Not sure whether it helps or not to the steering and how long it will the material last. The wood does not look so precise as on BUK. The drummer seat is very low.