FFXI - Poor Frame Rates Under Vista 64 Home PremiumFollow

Ever since installing FFXI on Vista I've had terrible problems with framerate issues despite having well over the required specifications. In normal areas I can keep a consistent 28-29FPS but once I enter any AH areas, parts of Jenuo, or areas populated by 6 or more players/monsters my framerate drops between 18-21. Below is my PC specs:

Windows Vista 64-Bit Home Premium SP1
ECS RS400-A Motherboard
Intel Pentium 4 (Prescott) 3.2GHz w/Hyper-Threading (Overclocked to 3.68GHz)
Crucial DDR2 1024MB RAM (2x for 2GB total)
nVidia GeForce 8600GT 128-bit 512MB DDR2 On-Board (180.84 drivers)
Standard IDE Drives (x2)

C: 3.12GB of 38.2GB
D: 3.03 of 14.6GB (Partition from 2nd Drive)
E: 3.60 of 22.6GB (Partition from 2nd Drive)

I have FFXI installed on my 2nd HDD on the E drive dedicated to only installed games. I know I don't have alot of free space on these but even before my drives were filled I still had these issues. Here's my FFXI settings:

1152x864 windowed @ 1280x1280 background resolution (3rd Party Windower)
Bump Mapping Disabled
Mipmap Disabled (Enabled via graphics card settings.)
Environment Animation Smooth
Sound Enabled (21)
Hardware Mouse Enabled
Compressed Maps Disabled

I've found by enabling mipmaps via my graphics it boosts frame rate by 1-2 frames, a minor increase. Additionally, lowering/increasing my window resolution or background resolution seems to do almost nothing. Overclocking my CPU barely has any effect with my CPU running at a steady 56-58C under excessive stressing. I can return it to default which will lower the CPU temperature but again, overclocking or stock settings don't seem to affect it too much. CPU percentages reach high 60's under standard usage when running FFXI and only reach full capacity when in extreme areas such as Campaign battles. I know FFXI has issues running under Vista at full speed but even my brother whom I got the motherboard and processor from never had this much trouble with FFXI under Vista even in windowed mode. I hope this is enough info to discern my problem, thanks.

EDIT: Vista rates my computer a 4.4 only due to the Calculations Per Second on my Processor, everything else is 5.0 or higher. And under FFXI Benchmark 3 I have a rating just below 4000.

Edited, Jan 7th 2009 3:22am by SamusKnight