Heya 
First off, this isn't a PC for myself, it's for my niece to play her horsie games on. The current machine she has doesn't have a GFX card, and her mum wants to buy a whole new PC. Therefore, upgrading options have been ruled out
The dilemma I'm having is between CPU and mobo (and possibly RAM, were it not so cheap anyhow).
A 2140 can be had for £40, and a decent mobo (Giga P35-DS3) for £70. That would have course be the overclocking route. A possible 2.5-3 ghz machine for £110.
However, a 4500 can be had for £75, and a cheap ECS mobo for as little as £25. That's a 2.2ghz machine for £100.
At a stretch, the 4500 + decent non-oc mobo is possible, if not costing more than £125 ish. That's assuming that there is a difference in quality/ stability between a £25 and a £50 mobo.
Whilst we're not talking about a machine to play Crysis, I will also be upgrading my own PC in the near future, so discussions of relative Crysis performance are valid
At the end of the day, I'd like to know which route is better - the oc route or the better CPU route. And whether a cheap mobo would be suicide or a good move. Doesn't need on-board VGA, of course, since I've budgeted £70 for that already.

First off, this isn't a PC for myself, it's for my niece to play her horsie games on. The current machine she has doesn't have a GFX card, and her mum wants to buy a whole new PC. Therefore, upgrading options have been ruled out

The dilemma I'm having is between CPU and mobo (and possibly RAM, were it not so cheap anyhow).
A 2140 can be had for £40, and a decent mobo (Giga P35-DS3) for £70. That would have course be the overclocking route. A possible 2.5-3 ghz machine for £110.
However, a 4500 can be had for £75, and a cheap ECS mobo for as little as £25. That's a 2.2ghz machine for £100.
At a stretch, the 4500 + decent non-oc mobo is possible, if not costing more than £125 ish. That's assuming that there is a difference in quality/ stability between a £25 and a £50 mobo.
Whilst we're not talking about a machine to play Crysis, I will also be upgrading my own PC in the near future, so discussions of relative Crysis performance are valid

At the end of the day, I'd like to know which route is better - the oc route or the better CPU route. And whether a cheap mobo would be suicide or a good move. Doesn't need on-board VGA, of course, since I've budgeted £70 for that already.