i'd say that since it is not question of which you buy, but which of those that you have should you use, i'd suggest the 2 stroke for all the reasons above. it makes no sense for you to use the 4 stroke when you have a more resilient 2 stroke lying around.

although i've seen a lot of four stroke trainers recently, i still think that a two stroke is better for the following additional reasons:

1. they are lighter - for the amount of power they produce, two strokes are lighter than their four stroke counterparts so less wing loading = better trainer or much more power. the 46 will be significantly more powerful than the 52 for about the same weight. the irvine is really about the power of a Saito 82.
2. they don't have as much torque - undoubtedly you will be aborting a lot of landings. the 4 strokes tend to torque the plane when you put the pedal to the metal. but then with the 52, it may not be that different. with a 82, you'll definitely see the difference.
3. slightly shorter props - well this might not be true with the 52. but with a power comparable 82, the props will be longer and more expensive
4. everyone and their mothers have run 2-strokes so you'll get a lot of support (wanted or not!) at the field. 4-strokes tend to be less understood.

but as you can tell from my handle, i'm a four stroke addict and really am running only one two stroke engine. it is also the sound and the mechanical complexity of the four stroke that won me over.