well i have got my tk-42 working fine off battery @ 1.6ghz using rmclock and semi stable @ 1.4ghz using my graphicbooster and mains.
You are going to have several problems firstly the choice of cpu is not only very limited due to heat constraints, socket issues, cpu availability and as i have found bios compatibility. I believe the only compatible cpu that is of the same heat output is the L510
I have upped the ram to 4gb, done the bluetooth, upgraded the hd to a 7200 rpm scorpio black and they all make small differences but none dramatic.
Interestingly if you upgrade the cpu and get it running at the correct clock you will also find that the memory and gpu clock will also increase which i found odd and a pleasant surprise - the speed difference in 3dmark 01 was dramatic to say the least! Although a word of caution, my system will not run @ full speed using the XGP - think there is an issue with bus speeds; despite the multiplier being used to increase the cpu speed.
Honestly dont think the fan upgrade will bring much since it is the size and rpm that make the noise rather than the mechanical noise.
My tip for the graphicbooster (Acer never actually produced a XGP unit) is to look on www.ebay.de - after a massive amount of trawling I managed to get brand new one from there for £40 all in.
Please keep us up top date with what you do - if you succeed with a cpu that doesnt require RMclock and runs stable @ full speed be very interested.
Which XGP box did you get? The HD3870 from Fujitsu Siemens?
AMD has been showing of a mobility HD5870 (desktop HD5770) with this laptop in tech meetings for several months now. I wonder why they never got it to production. I would easily pay 250€+ for this.
I would drool over a Ferrari One with a K665, a SSD and a HD5770.