Well fw4.0 sounds great, as have all the other FW's to date. I got my Axe around Fw6 or 7 and I don't recall the unit sounding anything but amazing...
I will say, that depending on the amp, and my ears, its not as simple as just changing the modeling version and having the ideal amp tone. I've found, again for my ears, that I've had to make a few slight EQ tweaks, change power amp hardness, tube type etc to get what I consider my ideal tone with regards to feel, tightness, cut etc. I've found that fw4.0 can take away a little harshness, grit, that to me sometimes sounds pretty good and "realistic", as I'm used to hearing some amps I've owned.
The feel difference is pretty subtle but going back and forth I think there is a touch more dynamics and tighter response with fw4.0, not huge, but when you get back to say fw 2.01 or something, its there. I perceive a little more immediate attack when I hit the strings.
Overall a great update, but one that I think will require a few tweaks, at least on the amps I've done so far. Once dialed in though, hot damn, does this black box ever nail the tone/feel of a cranked 100watt amp, but at any volume level...
You know that tone when your at a big gig, at soundcheck, and your able to have your amp running wide open, through say a favorite 1970 large check cab loaded with GB's, and the venue's got some pretty great acoustics because it used to be an old concert hall, and you grab your LP, hit an A chord and roll the volume up and it just roars and the sound fills the whole venue with this powerful "this is rock n' roll" tone" and the chord just rings and rings with that Marshally "kerrang" overtone, and as the notes die out into feedback you play a quick lead lick and the notes feel like that are just exploding off the fretboard, and there is this immediacy to the playing, that direct feel of fingers, guitar to amp, basically acting all as one, just like driving a vintage sports car, the shifter linkage, the steering, the gas, its all mechanical and direct, your driving a machine, your not pressing a gas pedal with a throttle-by-wire setup running your inputs into a traction control computer which is dividing the output to the 4 wheels, your simply stomping a pedal, opening a butterfly on the carb and dumping fuel into the engine which explodes and moves you forward....that type of feeling
Cool thing is that I'm in my den, playing through the Axe, and a CLR, at a pretty low volume, and yet I"m still getting that exact experience
Great unit