Shattered Kingdoms

1)Correct.
2)Correct.
3)Only magma spray ignores MR.
4)Magma spray ignores MP. It is the only damage spell that does this.
5)No, there is no damage spell that can be resisted by MR that is unaffected by MP.
6)I haven't played since the changes to enchant, but I think I have an understanding of current mechanics. As a general rule, don't go MR unless you have access to spell ward or are doing an MR barbarian build. Here are the pros and cons of going MR:

Pros:
-If you enchant for MR, you will only have to worry about how much MR you have. If you enchant for MP, you will need to have MP as well as willpower, fortitude, and maybe even reflex so that you can save against spells.
-MR can provide 100% immunity, while no amount of willpower will make it impossible for charm or sleep to land against you, no amount of fortitude will make it impossible to get petrified, and no amount of reflex will make it impossible to get locked down by bolt of glory. With regular saves, you can't hope to do better than saving against 90% of spells (my personal estimate based on experience). Having lots of MR can make it so you don't get an unlucky roll and dropped by an "I-win" spell.
-MR that you add to equipment stacks, so you do not need to find equipment that starts with MR. An MP suit would require equipment that started with saves (willpower, fortitude, reflex).

Cons:
-You will resist friendly spells, like heal.
-You need a lot of MR to actually resist spells reliably. If you do not have access to spell ward, or MR trains (only available to barbs), it is going to be extremely difficult to get enough MR for it to be reliable.
-You will not have willpower to help you break through someone's intimidate or sanctuary.

There are several other spells that ignore MR. Some are even hostile. It's not really appropriate to discuss them all here though.

Oooooo Baldy is getting called out by the village idiot! Someone pass me some popcorn and get me a beer!

Thanks for the in-depth response, Baldric. So... since I read in a changelog that voodoo is affected by MR now, does that mean MP would reduce its damage?

Styles, I understand. Hush hush and all that. Just trying to get a general idea.

How close can a sorcerer + full MR enchants get to 100%? I'm assuming you'd need at least some items that provide MR intrinsically.

Really easily. Sorcs can both enchant for MR and hold spell ward. It will be very easy to figure out how much MR gets you to 100% as a sorc.

Eddy, I can only think of one cabal spell that might ignore MR. And self-cast-only spells, of course. PM me with the others because I am curious.

Yeah, I'm not trying to be difficult; it's just that somethings are better learned IC and are inappropriate for discussion here (as you can see, even the veterans don't know the answer to this one). For an explorer sorcerer you might prefer MR over MP just because sorcerers can enchant for MR and cannot enchant for MP, but MR is not without its inconveniences. They can also enchant for reflex, which helps with the magma spray issue (not that you're going to encounter a large number of magma spraying NPCs in your journeys).

Ultimately, for exploration, this decision doesn't matter very much.

I always assumed by Dulrik's curious wording on the code update a long time ago that certain religious/cabal spells can bypass MR. I've not been able to check them, however. It's also possible that maybe earthquake or dig bypasses MR or something just for the lulz. Styles always has made it a habit to act like he's privy to something that other people don't know to make himself look superior, except that it usually turns out to be something of little to no consequence. My only other guesses are that maybe summon/gate bypass MR.

Summon and gate do not bypass MR unless the code has changed regarding them since I played. Aldric couldn't be summoned or gated to when he was wearing his MR set, even if he was accepting summons.

I don't know of any religious spells that ignore MR but I probably wouldn't know if some did. The druid damage spell might ignore MR, also.

I wouldn't be surprised if earthquake or dig bypassed MR just for the lulz, but don't know for sure.

Earthquake will affect a cutlass/halberd. But dont know if that is bypassing the MR or if it is the "ground trembling" and them being on the ground causing it. Didn't think to check to see if it damaged it or not.