Dieter Schaefer , Apr 08, 2012; 10:03 p.m.
I am planning to replace 18-70 with 18-200.
Why - this is certainly a step down in terms of optical quality.
Can't comment on the weather sealing - but if you are in a rough environment then maybe using some raincover or even a simply plastic bag might not be a bad idea.
I would not let the two batteries dictate which camera to buy.
If the small size of the D7K isn't a problem for you, then I don't see a reason not to chose it over the D300. Even though the D300 has the more extensive bracketing range and more AF points - these may or may not matter to you.