[Japo]

First of all, the advertised Hz rating is per core of course, so 2.9 GHz with two cores is 5.8 GHz total. And that's probably very obsolete (which series is it, Pentium D?): its power usage will probably very high (overheating). And you could end up paying the vintage price of a Rolls Royce for a Zastava Yugo.

A single core makes no sense whatsoever, it's like wanting a steam car. Clock rates can't be increased indefinitely because of heat, and the way to get more speed is to put more cores. Not to mention it allows parallelism, and this means user interfaces can respond to user interaction while they're performing long tasks in the background. It's very long ago that the industry moved away from single cores; and the later single core CPUs had hyper-threading.

You seem to go to extreme lengths to ensure compatibility with old games, and it's your choice. But what you want is a "new old" computer and that doesn't exist, single cores aren't being made any longer, you're very late to find out; I wonder if they're still making CPUs with only two cores instead of four at least, but I wouldn't bother buying them anyway. If you want something like what you have, repair your current computer; whatever's wrong with it, that's by far more doable than what you propose.

My opinion is that what you propose is absurd, for games and of course for every other purpose that you'll use the computer for. Issues when running old games can be worked out. And if you want an old PC besides your main one for old games, get an old one (or keep the one you have), because "new old" computers aren't sold anywhere.