Go Bonneville SSEi if you want the features and fun with SC motor. I likely sound biased since I had one, but they truly have the features and stuff.
HUD is a big one. Nice comfy seats, non self-destructing cupholders, self leveling suspension, onboard air compressor and ... a little sportier look than the Regal.
I also had a Regal and liked that a lot too, I liked it .... after I improved it though. Be warned if you go looking for the mod list on it, you'll be hooked by at least one of the things.
As for your trans. You could change out the diff (just make sure of the year it comes from. 4T60's changed pinions by year etc). Bonnevilles etc came with 3.05/6 or 2.86. You could toss in the 3.05/6 and have the best of it all. Slightly higher than HD trans and not as low as going 3.29's.