Maybe it's the honeymoon period talking, but I would definitely go for the LSS.
I just traded my LSC for an LSS. This amp is incredible. I've owned over 25 Boogies through the years and still own a few, but the LSS sounds the way a Fender should and you can get some really nice distorted tones as well.
I looked at the F series, and researched the 5:50 on the website, but they are nowhere near as versatile or organic in tone.
I wanted an amp that had Clean tones that would make me want to play, and I found it. It's been years since I had an amp that would make me wake up at 5:30 in the morning and sneak upstairs while the kids were sleeping to play.
I sold my beloved DC-3 and '66 Fender Pro Reverb to get the LSC because I had tried my friend's LSS and loved it. I had been trying to buy his LSS for a year. I went for the LSC because I thought that it would sound more like a Twin Reverb than the LSS. It did, but I had to reach a certain volume for the amp to come alive.
The day after I got my LSC, another friend called me up. He said that he had just bought the LSS from the other guy. You can imagine the words that came out of my mouth. I told him that I had just bought an LSC. He practically ran over here to try it out. In the end, we traded because he plays extremely loud and I wanted an amp that sounded great at any volume.
I think if you settle for the 5:50, and like the sounds of the LSS, you will be back. I've spent tons of money searching for the right tones and the right amps. Finally, I think I've found it. I have even modified most of my amps to get those tones, get the one you love. Take your time and try them both out.
It sounds like you have been able to use the LSS in a real world situation, instead of the music store showroom. Open it up, I'm sure you will find that it has enough power to pull off most gigs.
I used my DC-3 for about a year, with lots of different musicians and was never disappointed with the power it had.
If you are into Classic Rock, Rock, Blues, Country, etc. get the LSS.
If you are into heavier Rock or Metal, get the DC-3 and a Thiele cab.
Don't get the Express. You'll be missing out on a lot of extras, like Solo function or Graphic EQ.