Between those two, I would go with the Mark IV. Perhaps if I were getting the amp ONLY for the death metal stuff I'd go with the ENGL, but the Mark will cover those tones and then some. I'd reccomend looking into some used F-series amps as well. I use an F-30 for pretty much everything I do. I've used it on jazz gigs, country gigs, classic rock gigs, metal gigs, and I use it for all my fusion endeavors as well. It's probably got the best clean channel I've ever heard. The high gain sounds are somewhere between the Mark series amps and the Rectifiers. Great for heavy rhythm stuff, but I still always use a tubescreamer in front of the amp for my leads just to smooth things out and boost my mids. I run an EQ in the loop every now and then for a bit more fine-tweaking, but I've never once felt like I
needed to. The lower to mid gains sounds are really good and I've had a lot of luck getting bluesy/classic rock tones out of it, but of those two styles were my main thing I admit I'd probably go for something else. The only tone I really want that I can't quite get with the F30 is the lead tone from the Lonestar (think Andy Timmons :drool
. That's neither here nor there though as I'm sure the Lonestar isn't what you're looking for.
As for other amps to look into, I'd take a serious gander at those new Spider valve amps. I have this gut feeling that my hopes for that thing are way to high, but as good as they look on paper I really think they'll be worth checking out. Those would be WELL within your price range too if you're currently budgeting for a Powerball or a Mark IV. If you're into the used market at all, you could probably get yourself a triaxis, poweramp, and a decent cab as well. That's one of the most versatile rigs you can get and you'd probably even have some cash left over to put towards an effects unit and have yourself a good rack setup. The Road King, as J-dub mentioned, would be a pretty solid and versatile setup, but the rectifier tone might not be what you are looking for exactly....and the upkeep on those things is pretty intense. If you get bored one night, go onto the mesa boogie website and calculate how much a total re-tube of that amp would cost.
If you're planning on going with a head/cab setup, I reccomend saving some money and going with an Avatar cabinet instead of whatever brand the head is. Sure, the logos wont match, but those cabs sound fantastic and save you a ton of money. They do look pretty nice too.