Post-boot use of faster storage

Thanks to this forum, I have a working Dockstar with Debian :)
However, I could not get my fast USB harddrive to be my boot host, it was too slow to spin-up and would boot say 25% of the time, but I have a 2GB USB which boots reliably. I am using the harddrive for data a post-boot mount, that is also working reliably.
What I'd like to do is remove the OS cap of 2GB, move SWAP and other performance-sensitive functions to the harddrive.
I'd like to basically put a load of edits in the /etc/fstab to begin using the harddrive as early as possible. I know how to do this, in terms of say copying /usr, /var, /lib etc to USB harddrive and place lines in the fstab, but I want some help on when I can do this.
If the USB harddrive is not ready to be a boot device, will it be ready to mount any of the above critical directories?
Right now, the very end of the boot process I have in /etc/rc.local some mount statements to mount. If I place mounts in the fstab that will bring it much more forward in time.
Which can I safely move into fstab?

So far, I've played safe. I've added a higher priority swap via editing rc.local

tail /etc/rc.local
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

mount -t ext3 /dev/sdb1 /mnt/SG500G
swapon -p1 /mnt/SG500G/swap

exit 0

Which seems to work

root@dockstar:~# swapon -s
Filename				Type		Size	Used	Priority
/dev/sda2                               partition	361452	0	-1
/mnt/SG500G/swap                        file		327672	0	1

What else can I do. My 500GB /dev/sdb disk is faster at sequential, but slower than my flash /dev/sda for random, benchmark results.

Benchmarking /dev/sda [1987MB]
Results: 652 seeks/second, 1.53 ms random access time
Benchmarking /dev/sdb [476940MB]
Results: 38 seeks/second, 25.84 ms random access time

root@dockstar:/tmp# sudo hdparm -t /dev/sda 
/dev/sda:
 Timing buffered disk reads:   32 MB in  3.08 seconds =  10.38 MB/sec

root@dockstar:/tmp# sudo hdparm -t /dev/sdb
/dev/sdb:
 Timing buffered disk reads:   64 MB in  3.03 seconds =  21.09 MB/sec

I don't know the bootloader internals.... but according to the uboot manual (http://www.denx.de/wiki/DULG/Manual) there is a sleep function available. So if you add a 'sleep 5;' in front of your bootcmd your drive gets more time to spin-up.

I don't think these (25% wasted) 5 secs will matter.