I don't have a link for you that can explain the differences between the versions, but I can give you my opinion on them.
Sense 2.1 has less lag than 3.0, 3.5, and 3.6. You're familiar with this version if you've used your Bolt for any amount of time. I believe the other versions have everything that 2.1 has, and if they don't, then I didn't use those features.
Sense 3.0 has a 3D look, with the home screens rotating in a cube animation. Plus, if you scroll screens to the left or right, they will wrap-around and keep going. (Many of the 2.1 ROMs have included this feature as well) 3.0 has new and different widgets which are nice, but I feel like I have to overclock to overcome the lag that accompanies this and 3.5. OCing isn't that big a deal though, so I like 3.0 and 3.5.
There's not a huge difference in my mind between 3.0 and 3.5. I think 3.5 is a little easier on your phone's resources, and some of the widgets look slightly different. I still get lag on 3.5 but OCing makes it so I don't notice it much.
I'm sure I'm forgetting/overlooking some features, but this is what I can think of off the top of my head. Plus, I'm not always sure what's a part of the ROM and what's standard with Sense. For instance, many 3.0 and 3.5 ROMs come with Beats, but not all do. Infected Eternity 3.5 has a cool clock widget that BAMF SoaB 3.5 doesn't. That's why I recommend trying a bunch of ROMs so that you can find the one that you like the best.
And if I've forgotten something vital, hopefully someone else can chime in and share.