Well, there are lots of opinions on this but you really need to try before you buy. Based on my own experience of owning a TX in both calibres I would not necessarily agree with points 1, 3, 4 and 5 (above).
I've never managed to get within 20 yards of a magpie or crow though... magpies seem to drop very easily; crows much tougher.
The best solution is to go for a .20 of course