I'm going to repost something i wrote last week in the general thread about this very thing, except about the Droid X to an Inc4
I got mine yesterday and unfortunately it has a hardware defect in the prox sensor, so I'm getting a replacement delivered to my door sat morning, go verizon!
However that sensor issue only affects phone usage while in a call so I've been playing with it quite a bit. I don't know how many people are coming from an much older device like me but i thought I'd share my exp so far.
I'm coming from a Droid X with Liberty flashed.
First impression was whoa this phone is small compared to the X. But as soon as i turned it on and started playing with it, the screen was so beautiful it didn't matter. The Inc screen is .3 inch's smaller but because of the higher resolution you actually gain screen real estate. The best part about the size though is my hip case is .5 inchs smaller, which doesn't sound like a lot but trust me it is!
Call quality is much better than my X as well. Perhaps it's just because the speaker on the X is 2 years old now but people sound much clearer to me on the Inc.
I haven't really had a chance to mess with the 4g data as i was on wifi when i setup my accounts. I will certainly play with that more when my new one shows up tomorrow.
The OS is extremely snappy, i haven't had a single hitch yet. I think i'd still prefer a AOSP rom once they come out but so far i love Sense 100 times more than Blur and will be happy to run it for the time being.
Last but not least, unlocking and rooting this thing was extremely simple, thanks most in part to our excellent devs. I remember working on my X for an hour before i was ready to install a custom rom. Granted i was brand new to the scene, but getting custom recovery on the Inc just felt easier.
I'm extremely excited to start using this thing full time starting tomorrow!
Now that I've gotten to use it for almost a full week now I'm that much more glad i got one. I looked at the specs and the thunderbolt screen is the same size as the Droid X with an ever so slight reduction in resolution. I personally haven't noticed any difference with the screen size. In fact everything is so much more clear and crisp.
The 4g data is great as long as your in an area that supports it, although i'm on wifi 90% of the time. 4g is a little spotty around my house (most of the time 2 to 3 bars, i've seen it swap to 3g twice), but where i work it's full bars, and quite fast. Surfing the web vs my X is much quicker now.
As far as the speed of the phone it's like night and day from the X. I always felt the X wasn't as usable until i threw a custom rom on it. That made an amazing difference for me, and now using the Inc4 i get the feeling again and this is with a stock rom! I can only imagine how fast this thing will be once i finally pick a custom to stick with.
My reason for getting an Inc4 is a little different from yours. It was forced on me because my X's charge port is starting to die. I thought i'd be sad to see it go, but honestly once i got the Inc4, i couldn't go back