Archon? Haven't played wizard at that level, watched some streams and I think you'd need a lot more than 500 mil to be able to farm 5-7 fast. Barb is the answer. You'll definitely farm faster than any other class.
I prefer 100% WotB uptime Hammer Barb with Sprint (Marathon rune)
Im farming mp5 relatively fast (20-25m XP/hour with no XP gear/gem) and can play mp7 keys/ubers easily. My gear was not so good it was bought some time ago for around 100m only and there are some MF pieces as well. (110k dps/ 210k buffed)
I tried other classes and builds as well with good results but this spec is my favourite (edit: WW probably faster but dont like:))
You will not be able to build an Archon wizard with 500M that can efficiently melt through MP5-7. One thing you need is a high DPS, life steal and socketed fast one-hand weapon. That on its own will eat your 500M budget or more.
You'll have a better shot with CM/WW wizard or standard WW/Sprint/HotA barb.