I just said that it makes no sense for him to change to such a system if he wants to upgrade, because clearly even his 4850e is faster than the fastest available atom cpu (or a comparable cpu from AMD, like the e-350).
I also didn't ask him to buy a new cpu+motherboard, i just mentioned that it might be worth a thought.
Anyway, here some interesting test results (sorry, it's in german, but I think the graphs speak for itself):
We are talking about 26W difference already in idle (2500k vs 1100T). And that's without any undervolting. Under load there is a difference of more than 100W (!).
So I think it's definitely worth thinking about spending more money and take the Intel system.
Of course, if he doesn't need more performance anyway, there is no need to upgrade. Then he should keep his current cpu and buy a cheap geforce card, like the GT430 as you mentioned.
If he wants and/or needs more performance then he should consider the Core i5 as a possible alternative to an AMD hexacore.
Nevertheless, in both cases there is simply no need for an ATOM-like system.
By the way, you really want to recommend an ATOM/ION system to someone using gentoo?