Well.......Lets discuss the NM thing....
It depends on many things the armor(I will tell about A grade ;>) you are going to choose for your sps.
PvE:For the pve stuff i would choose a NM set for my sps,followed by a +4/5 int -4/5 men dye.You will have a lot more matt so you will maybe save some Mp which is the main SpS problem.

PvP:Here things are kinda more difficult to choose.
If you are able to have a BD always with you for the pvp and maybe PoW,i would get a NM robe.With full buffs you will still have plenty of cast speed and good matt.example: 74 sps nm robe/som +3 acc/maj unsealed set/2x wit+4 men-4 dyes/full buff/dance/pow:MATT:2225 castspd:1236 mdef:958 not bad !!!
while with dc set:MATT:1954 castspd:1729 (fcuk me !!!!!!!!) mdef 939.
MUCH BETTER!
without the dances/pow, still the DC set is FAR better than nightmare.

conclusion:The greatest thing of the sps is it's castspeed. DON'T RUIN IT FOR A FEW MORE MATTACK!!!

-Subclass:I suggest you to become a warlock.You will have easy solo exp with the cat buffs using MAJ robes and Duals (kesh-kesh +4 for me!)
You can join a fighets/rangers party and use the really usefull kitty buff as well.
At the pvp's(before c5) you will be a very usefull player.The cats have really good stats and they cause a lot of damage.
After C5,erase spell will be your nightmare.Just you have to wait for the others to kill the buffers,so they won't erase your kitty:P

I think i helped you,
Have fun above all:>

i'd say warlock is better with mage weapon not duals because later on the damage from duals or other fighter weapon is shit.your main weapon is kai not dual kesh

main weapon for pvp's of course will be a SoH/Sov-WTear/Som(all + accumen )

but, in PvE, a warlock can use the duals.
If you are not using L2walker,switching to a weapon with accumen Sa will be good for buffing/healing the pet.
If you are using L2 walker,well...you can either use only som(etc) and keep on watching and healing the pet or use only duals ( lately i've been trying DS/Kris/Bloody orchid (+ sa focus) tiz really cool!) and spend some more time for buffing and healing for a few less HP.
Anyway...most of the summoners prefer the first way for pve.I'd choose the second. You can chooose a third one

Have fun:>

I think with duals the cubics are more effective (or I think so) and they use their effects more often. So, I would choose dam*dam or tallum*dam (in interlude).

but the damage dealt by duals is nothing compared to the damage dealt by your summons so i'm still sticking to my point about using mage weapons.cast speed and matk for heal are really needed

I have to disagree with SirAdrian about the armor , What u want to do to maximize your matk and make 1,5k damage in a second or maximize your cst.spd and make 2 skills each of 1k damage in a second ?^^

SpS + Nightmare = sux
SH + Nightmare = still sux as long u want PvE armor and the perfect choice still reamains demon's set(+4 int)

Nightmare

SPS = 20 % m atk wich it's nothing acording to
SH wich have 24% m atk in plus

Demons

SPS = 25% m atk
and on SH = 29%..

Don't put m. atk armors on mage classes wich are based on wit ..
SpS isn't meant to wear m atk armors because if u'll make him like that
then he will become a piece of sh** nuker.
And trust me.. instead of make'ing lvl u always spent u're time about
"war/dead/to the hideout ; war/dead/to the hideout if u see my point"
Always wear BW/AVA + Demon's or DC + Demon's and make 2 macros for quick equip.. and dunno..

go for it