full spr will provide the same buff strength as full int for swell arms, enchant lightning and fire. But if you are thaum c3, swell brain will give you more total magic attack than a full int build.
If you want to increase your AA speed then get chrono c3.
I still actually recommend going full spr instead of full int because it will help your enchant armour shop. Chrono 3 gives pass which is one of the best support skills in the game.
I do not recommend going runecaster. Rune of giants might help with auto attacks but it brings almost nothing to team in terms of support and you cannot cast any skills other than wiz c1 to c3 or RC skills while in buff. Rune of giants stomp damage is based on magic attack.
Rune of protection is bad and trying to cast damage skills without surespell is hard.
Overall i recommend pyro c3 chrono c3 enchanter.