Would you mind posting after you compare the two? I've been looking for a media player to replace my wife's aging Archos 605 wifi. The Galaxy player series looks nice but I wanted something mod-able which the 4.2 doesn't look like it's it.
I've really been trying to decide between the 5.0 and the 4.0 so I can run a custom rom.
I just picked up a 4.2 today, I think I will keep it and wait till the talented moder's here to come up with something nice for it. The most important thing that I decided today was that I can live with it the way it is out of the box so any enhancements that becomes available later is just gravy.
Compared to the 4.0 it feels a lot more "current", which I know is a highly subjective opinion but the 4.0 with the rounded corners and thick chrome border/bezel it reminds me of the old iphone which I hated.
Also the 4.2 run 2.3.6 vs the 4.0 running 2.3.5. The 4.2 has a newer version of Touchwiz which is much better than the one on the 4.0.
The media player on the 4.2 is also a newer version with some DSP features not found on the 4.0.
The 5.0 runs 2.3.5 so it should be pretty similar to the 4.0 since they came out at the same time.
I personally think 4.2 is the best overall size for my application which is an mp3 player for while I'm driving. I checked out the 5.0 at the store today and there is no way I can use it one-handed which is a deal breaker. Also, I already own a tablet so I really don't need the extra screen size on the 5.0 in a mp3 player.
If you live close by a Best Buy you should just go and play with all of them.
Cheers.