After you get your new ram, try it without using a divider first. The divider will impact your performance so don’t do it unless you need to, a 1:1 between cpu and ram is best. Some inexpensive DDR400 can run at 227fsb, but like rdgrimes said that’s over the limit for alot of the cheaper memory. I had some Kingston valueram DDR400 that I got up to about 230fsb before instability, now I have much better ram though. Some ram may not even make 220fsb though, it just depends you have to try . At a 230fsb, the ram is running at 460Mhz, so DDR400 is sorta pushing it unless it’s really good quality ram maybe.
Even if you can only get like 225fsb, I’d still rather run like that than put a divider on. Divider should only be used if you can reach alot higher fsb with your cpu than your ram can take, only then will it benefit you performance wise at all. But if you can only reach a tiny bit higher fsb, like 227 with divider vs 225 without, it’s better just to run without divider. Now if you could get 250fsb with divider but 225 without, then a divider would be worth it for sure. But personally I’d still buy ram that could take that 250fsb so I could run 1:1. Remember your ram is how the cpu talks to everything, making it run slower creates a significant bottleneck depending on what you do with your pc. Just for example with gaming, where alot of bandwidth is better, running a divider could very noticeably impact performance. But doing something else where high bandwidths aren’t required, the impact may not be so noticeable.
If you wanna be able to reach your max cpu overclock and be able to run 1:1, I’d recommend getting some DDR466 or DDR500 memory if you can. Up to you though, if new ram will only get you 2 more fsb or something while running 1:1, you have to question whether it’s worth it or not. Just don’t run a divider so you can get 2 more fsb though, it’s not worth it. And maybe you’ve heard this, but sometimes it’s not always good to run mismatched ram modules. It may work just fine in most or almost all cases, but they can have different timings, different voltage ranges and sweetspots, etc and can be a problem even if you’re not overclocking. Sometimes two different rams just plain don’t like each other, it can happen.
Also, I’d recommend Prime95 for testing system stability, you need to run it for a full day or more to really know you’re stable. It stresses both the cpu and ram and should catch any errors (unstable overclock, bad ram, etc.) And memtest86 as already suggested is a great one for testing ram, and same thing with that, don’t run it for 1 hour and think your good. You really need to run any program like those for several hours or days to know you’re rock solid. If you can run memtest or prime for an hour, it means your more than likely stable, but not for sure. And watch your temps too if your overclocking, heat is the enemy and a killer.