Vert/Solaria are damn close for a 65 mage that raids and occasionally solos/pet-groups.
Yes, keep it very clean and clear -- casters are constantly checking the status to make decisions on what to cast and when.
Spell bar -- needs to be obvious when refreshed. Solaria seems better than Vert was on this. No spell names, just clear icons. If you are using your mouse to click to cast, you are *off* any raid I am leading immediately. Post-patch now, make the spellbook button easy to right-click so I can quickly get the pull-down menus if I need to quickly create a new set. Make the gems big enough so I don't miss if I need to swap out a single spell.
Spellbook -- What's a spell book?
Everything now is
/mem setname or right-click on an empty icon.
Casting bar -- MUST have clear marks at 10% and 20% remaining for chain-casting pets. For 5-second pets (max hasted), 20% is one second. For 10-second pets (typical, without AAs), 10% is one second. MUST be the same width as the mob health and nearby so I can make a duck/switch assist/cast decision.
Key Information: Casting time, mob health, mana, pet health. Make these bars the same length, vertically aligned with each other. All (except casting time) need NN% for a slew of reasons.
My health? Yeah, curious, but really not my worry. Just put it somewhere where I can glance at it quickly. If I am getting hit, just let me know when I have to give up on waiting for the mez and take other action.
Stamina? Hmmm. What is that for again?
Hotbuttons -- make them large enough so I can clearly see what my clickies are. Give me access to a few of my bags and slots (customizable) right there so I can swap them out mid-battle as needed.
Socials -- I keep all my pre-made
/assist MT_01 keys there. Need access to them if we get to a third-line MT. Small is fine, just large enough to be readable.
Buff bar/bard bar -- "glance-able" icons. 14x14 is probably too small, 22x22 is plenty big. Need names clearly there, as well as a very obvious way to see beneficial vs. determental. Need a slot-indicating thing so I know how many slots I have open.
HP/Resists -- about the only player stats I need to be able to glance at. Quickly tells me if I have drifted out of bard coverage, lost a buff, or forgot to swap back in a main piece after using a clickie. Weight is useful, but I have all 100% WR bags, so I am not one to comment.