I also have two Thunderwear holsters which are excellent for deep concealment and I have carried both a G30 and an XD9 at the same time in one. That would be the way I would go if I really wanted to wear a particular shirt that was too tight.
Over the last year I have been deliberately buying shirts that are a size or two bigger than I would normally get just for concealing better...honestly it isn't due to weight issues :)
I also have OWB holsters but I can never conceal the gun in that because I am too narrow shouldered to hide the gun at 3 o'clock and I can't wear it at 5 o'clock and draw the weapon very easily.
Hope this helps but I echo what was mentioned earlier and say that the best thing to do would be to try and see what works for you, holsters are pretty much a personal choice.
