SSD in Mac Mini

So I put the new ssd in and external case connected via usb 2.0 and imaged with snow leopard... Bootup time via 2.0 was 20 seconds faster than factory hdd... Then when I installed in the mini , bootup time was only 7 seconds faster than factory
Any suggestions, reasons and comments are needed ...
THANKS ZR

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Early 2009 2.0ghz 4gigs of ram... K so after I posted last night, I tested one last time and boot time dropped 4 seconds... I saw the post this morning and repaired disk permissions twice.. still same result.. Factory hhd boot time 47 sec... boot time before post 37 sec ... after 33 and when connected via usb 2.0, 27 seconds