Building a new high-end computer.

if you're a big overclocker, the difference between the manchester and toledo cores might be more evident. toledo probably overclocks better, and it is newer. if you're not really big into overclocking, i'd get the 4200... unless the extra 2x512kb cache is a big thing for you.

this article has benchmarks run with the x1900 all-in-wonder that you wanted.

ram from those manufacturers should be fine, though i'm not too familiar with g-skill memory. timings matter, but not a ton: the 500mhz speed over the 400mhz speed of the default ram would negate anything timings would change (except maybe small chunks of data being rapidly transferred, but you wouldn't see much difference except in simluated benchmarks). however, if you can get ram that supports lower timings (especially CAS latencies being below 3), then go for it. every little bit helps, right?

Jam it back in, in the dark.