I have a '09 2.26 octo with 6 gb ram standard. I'm finally deciding to upgrade the RAM but don't want to spend a ton if possible. Is there a benefit/downside to just upgrading 1-2gb stick or 2-2gbs as opposed to replacing all of the 1gb sticks with 2 gb sticks? I've seen the benchmarks for the various memory configs but nothing where things get added piecemeal. Thx.