motherboard question follow up

[muppet]

Me again.

This is my specs,

hp pavillion a1626n,although i have upgraded almost everything in it.

250gb hd
amd 64 x2 5400
3gb of pc 4200 ram
8800 gts 640 mb
x-fi extreme music
550 watt ps
plus a new case

The reason i asked about upgrading the mobo was for 2 reasons,the first being that the bios does not display temps so i cant tell hot hot my cpu is running at and the second reason being that a bigger mobo would allow for more room between the video and sound cards for better cooling.Another question i have is i when i run 2gb of ram (2x 1gb sticks)i get a index score on vista of 5.9 for ram but when i use 3x1gb sticks my score drops to 4.5 i think this is because its not running in dual channel mode with the 3rd stick?so i was going to buy another gb for a total of 4 x1gb sicks to put in 4 slots ,,,,would this put me in dual channel again?I know vista wont read all 4 gbs but i dont care as long as it puts me back in duakl channel mode.Alo hp says i cant upgrade the cpu to no more than the 64 x2 5400 as i have done but i was wondering if anyone else that had the same pavillion a1626n has done so or can it be done as i wanted to get a 64 x2 6000 2mb cache.
I have no trouble running sh4 but am always tring for the best machine i can get.

Thanks for your help ,the reason i ask in here as i know there are very smart people here that know more about pc's the hp support ever will.