You think you're old? I still remember using KDE3, hell no X at all even (back when we could browse with elinks without missing much). Those new-fangled DEs...ooohh. I would just not mess with the kernel (I shouldn't talk though ) if you want no troubles. Just strip the initramfs, use systemd, e4rat if you're still a non-SSD user, bam, 5 second boot.
Regarding 5-second boots, I tried compiling the Zen kernel. No change though. Then I downloaded the fastboot scripts. Broke something (I forgot what), and are deprecated now, apparently. Eventually, I just stripped everything irrelevant to me out of rc.conf such as iwconfig (I used Wicd) etc. and got a satisfactory time of ~12 seconds. good enough for me, imo.