FFXIV consistent FPS but appears jerkyFollow

The problem I'm having happens specifically when I run the game at the same resolution as my monitor: 1680 x 1050. Anything lower, and the problem disappears.

The problem: The motion of the camera when I'm running, etc. appears jerky to me. The FPS and other stats that I'm monitoring on my GPU and CPU are exactly the same when I set the game resolution to 1600x1024 vs. 1680x1050. The game just appears jerky at the higher resolution, which matches my monitor. This happened in the closed beta, open beta, and now also in retail. Any suggestions are greatly appreciated. :)

My computer specs are:
AMD Phenom 9550 Quad-core (2.20GHz)
6.00 GB DDR2 RAM
Nvidia 9800GT 1GB
Windows 7, with Aero turned off while in game

Settings in FFXIV Config:
Windowed
1680x1050 (anything smaller and no problems)
4x MSAA
Buffer size: resolution
Shadow Detail: High
AO: off
DoF: off
Texture Quality: High
Texture Filtering: Highest

Also, I bought a 2nd GTX460 graphics card (an MSI Cyclone 1GB) when my husband and I built his computer last week. I will probably try to upgrade to that card from my 9800GT. The specs on the card say it requires a 450-watt power supply. I have a 500-watt. I guess my question is whether the recommended amount is generally enough, or am I going to run into problems with only a 500-watt power supply?

Edit: I just realized I was wrong - I only have a 400-watt power supply, so I guess I won't be installing the gtx 460. Anyone have a guess on the reason for the jumpiness in the game?

Edited, Oct 2nd 2010 7:51am by LuthienOfSeraph