Hi, just my 2 cents worth here
Everyone likes different kinds of sounds, some prefer colored sounds and some prefer neutral sounds. For me, i like the K701 and HD650, and i will stick with them for the foreseeable future. Though i've had friends who have tried those 2 and the dt990 and still prefer the Grado MS1i that i had.
Although in speaker design you do aim for a flat frequency curve, everyone listens to music from a different perspective, so it's up to you to decide which kind of sound signature you like in the end. Cause in the end, it's going to be you listening to the headphones.
Now, onto the Beyers,
1) There wasn't any noticeable difference in sound in the pro and premium versions that i could make out.
2) I've went through a few headphones before i found something that i really liked and sticked with them. I would suggest that you try out a few more headphones before making a choice. Have you tried the Grados? They are known to be really good for rock, you could also try the HD600, those are quite well-known.
3) The differences between the 250ohm and 600ohm versions are miniscule, They did some blind testing on Head-fi and those that could tell the difference preferred the 60Ohm versions, but stated that there was only a very small difference if you really really listened into it. if you have decided on the beyers, then just try them out and then decide.
4) You'll definitely need an amp for the Beyers, especially the 600Ohms version. You could consider the Govibe Peak, but also look into other amplifiers, you could look for one in the classifieds section. Personally i think that buying an amp first hand is quite expensive. You could get the headphones from B&W if you don't plan on getting the Go-vibe Peak, but otherwise, the extra worry about the warranty and shipping is a bummer, and when you decide to sell it off, some people would prefer a local set. The price of the Beyer alone at Jaben is more than the price of the bundle at Jabens. Weird.....