Level 2 vs Level 4

If you're not playing a dirt cheap army where it makes no sense NOT to take a level 4, I don't think taking level 4s is the no-brainer that the internet seems to suggest it is. Perhaps it is my bad luck with miscasts (for my opponents also), but in my experience going overly heavy (reliant) on magic in low level games (sub 2500) is just putting all your eggs in one basket.

Multiple low level wizards has the benefit of spreading the risk of miscasts and also means you don't have to go all out to wrap up your squishy point sink in cotton wool, usually involving spending even more points on magic items or bunker regiments.

I don't have the table unfortunately but I would guess the dispelling is not that different because you generally roll however many dice you need to. The benefit of a level 4 really is getting off more low-dice rolls in terms of casting, which in turn draws out more of the opponents dispel dice.

It depends on which army I’m using. If I’m playing Empire I like 2 level 2s with different lores. When I play VC/Undead Legion I go for a level 4 Vampire and 2 or 3 Necros (level 1 or 2).

I have to go with the old dogma here Lv4, for two reasons: That extra +2 on dispel is pretty critical and the extra two rolls for spells make it a lot more likely that you will get something useful to cast. Would love to see that table though so I can change my mind.

Hmm, the only math table I have seen in this regard was for runesmiths. In most friendly games, we usually stick to the 6th edition rules for unit selection. So, that precludes a Lord below 2000 points anyway.