difference between PC2 5300 and 5400?

I don't see any difference except for those 5300 and 5400 number, and on other online store sites the 5400 is sellable as an upgrade option for intel Mac.

Make sure you bought it from the site that stated clearly for Mac Book support and have an easy return policy if your memory fail or incompatible.

One other thing, I believe it only term of the memory manufacture categorized their product because the excact number are 667 x 8 = 5336 and the manufacture to put the number round it down to 5300

And on the other hand the pure 5400 contain chipset that runs at 675 mhz so 675 x 8 = 5400, but it downward compatible with 667 mhz. so it also save for your mac book

It's just a trick to attract your attention - each of this modules works on 667 MHz speed:
http://www.gskill.com/Flash/en/f2-5300phu1sa.html
http://www.gskill.com/Flash/en/f2-5400phu1sa.html

I posted one of the reviews on NewEgg's site. I assure you, it works just fine.