I moved from the EVO III to the EVO IV and found that the IV was a much fuller sounding amp, with a lot more flexibility, power and general presence. The lack of floor coupling could have also been a factor though.
The step up from the EVO IV to the EVO V is smaller in terms of general character than the step from the EVO III to the EVO IV, but I would say that the step up in headroom and overall power/volume is considerable. I would also say that the EVO V has taken a little more getting used to than the EVO IV. I found the EVO IV to be a very natural 'plug and play' get what you want sort of amp, but the EVO V has taken a little more taming and fiddling to get the sound I want. The sounds are all there, they just take some coaxing out.
To be fair to the EVO V though, I have less time on it so far, and have also changed my cab as well, so it could just be about getting this one to play nice with the 610 rather than the NEO 210 I used with the EVO IV for a long time.
Overall, the EVO IV is a phenomenal sounding amp, and unless you really need the headroom and power of the EVO V, it can do everything you could ever want and sound brilliant every time.