I would have thought that the extra mhz would be minimal between 3400/3500.
The L1/L2 caches run at the same speed of the processor, so for the sake of a 1or 2% increase in cpu, i would go for the cache.
Although at these sort of speeds, it probably wont be noticeable which option you go for, unless you are a stickler for benchmarks.
Does it matter whether it takes .0089 seconds to do a calculation, or .0088seconds?
;-)