IRQ16 is sharing components, is this bad for performance?

I am using a P4 prescott 3 GHz on a 478 MoBo with a Geforce 6600 ultra graphics card. I noticed that my AGP graphics card is sharing the IRQ16 with 2 Intel 82801EB USB Universal Host Controllers (at 24D2 and 24DE).

Will this interfere with my maximum performance for my graphics card? If so, how can I re-assign the USB controllers to another IRQ? (I want to leave my graphics card at IRQ16. )
Sometimes when I am using Flight Simulator FS9, I experience stutters in the 3D mode (Virtual cockpit) and was wondering what could be causing this.

Sofar I cleaned up my Window XP Pro, scanned for virusses and spyware, defragged my HD's and set up a second page file on my 500 gig external disc (F800), optimized XP for max performance, set the CPU to affinity CPU0 and modded the FS9.CFG file for max performance.
Windows has the latest SP2 with all updates, latest BIOS installed and latest chipset drivers, latest graphics drivers, latest sound card driver.

Anyone?