FYI, my professional background is web development and management, i have several sites that rank in the top 1-5 for pretty competitive niche keywords and they have stayed there for over 7 years straight, so i have a good idea of what works and what doesn't.
I dropped out of the professional "league" around a year and a half ago. So I know where you're coming from. But even with todays amazing speeds I still have that demon on my shoulder called "perfectionist" nagging me.
Honestly I think page load speed is already implemented in Google page rank since most first page results show up faster than say- 10th page results. Although that could just be from different budgets in quality hosting.
When I work with CSS I generally have 8 development CSS files
- reset.css
- layout.css
- color.css
- typography.css
- ie7.css
- ie6.css
- ie.css
- scratchpad.css
My reset is really a dual-use of reset and "unreset" or basicly setting my own person defaults. the middle 5 explain themselves and the last one scratchpad.css is where I develop in. I work on one feature at a time then split it up into the appropriate css file once I get it working in all browsers...one feature at a time (header > left side > middle > right side > footer)
My JavaScipt I do a similar scheme. For example, when I set it up like this.
then any specific javascript addons like if I need Javascript for the navigation I will make a navigation.js, if I need something for an ad banner I'll make an adbanner.js, etc.
My images I also like to do the same, when working with them I have them all seperate but then when I'm finished I modify the css to work with an image sprite. 1px backgrounds that repeat-x in one, 1px background that repeat-y in another, all the graphics including hover, blank, active states as well as the logo in another. Anything that needs an alt tag will be seperate.
Finally I take all my CSS, remove any comments, whitespace and check for any shorthand rules I can use- same with my javascript and then I take my sprites and images and compress them as much as possible (usually they're PNG's) and run the site from there.
I save about 30 server request, and 40kb on average which is about 3 to 5 seconds. Pretty much it's all up to render time and the webhost itself after that since there is almost no room for optimization once I'm done with my clients...or, ex-clients I guess.