Can a Magus use Spellstrike and Spell Combat with spells prepared with other class slots?

Question

Let's assume we have a Magus 2/Wizard 10 who wants to cast Vampiric Touch spell on an opponent. The character has prepared the spell using one of the Wizard spell slots. The description of Spell Combat and Spellstrike only requires that the spell is on the Magus spell list - which it is. (Failing that, we can assume the spell is being cast using Broad Study magus arcana, though that would elevate Magus level requirement to 6).

Can a Magus use Spellstrike and Spell Combat to deliver Vampiric Touch prepared with Wizard's slot?

Answer 1

First, an official source: Magus, Spell Combat: What spells can I cast when using spell combat?

The spell you cast when using spell combat has to be a magus spell you know, and it must be a magus spell prepared with one of your magus spell slots.

It's pretty clear: you can't.

About broad study:

(Other magus abilities may modify what spells can be used with spell combat. For example, the broad study magus arcana explicitly states the magus can use spell combat to cast spells from the selected non-magus spellcasting class.)

This is less clear, but it seems to say that you can use your vampiric touch with wizard slots.

Answer 2

Both spell combat and spellstrike are limited to “spells on the magus spell list,” but in both cases it doesn’t matter what class’s spell slots are being used to cast them as long as they are on the magus spell list. So a 2nd-level magus/10th-level wizard could indeed prepare vampiric touch as a wizard spell, and since it appears on the magus spell list, use it with spell combat and spellstrike. But he could not do the same with touch of blindness, since that spell does not appear on the magus spell list.

The Broad Study arcana, however, would allow the magus/wizard to use touch of blindness with spell combat and spellstrike. But the Magus 6 requirement kills this option’s viability; the addition of weapon damage is not remotely worth that many spellcasting levels.