Well, memory timings aren't as important as they used to be with pc100-133 mem, so I wouldn't really worry about the tighter timings a whole lot.
What vid card are you using? I'd go for the higher clock speed if it's a 9700/9800, as they really thrive the more you throw at them. Otherwise, I would suspect that you wouldn't gain much by doing it, and toi leave a stable, good system alone.