pasky2112, when you get your G20, pull the barrel out, and drop a round into the chamber. Take a look at the feed ramp, and notice how much of the round, above the extractor groove is exposed. If it looks to be excessive, that may be a problem with hot loads. If it looks only marginally, more exposure, from the rest of the brass, you should be fine. You won't know anything for sure, until you have ran some rounds through it. If you see bulging in the factory PMC ammo, the bulge will be worse with hotter loads! Again, you will need to fire the G20, before a decision is made to whether or not an after market barrel is in order.
I do not shoot 40 through my 10MM's! I reload, and sounds as though that is in your plans also. If that is the case, there is no reason whatsoever for a 40 conversion barrel.
If guns kill people, then, I can blame my pencil on my spelling!