I wouldn't call the 600 pocketable, while the 300 seems more so (although I have to admit, I wouldn't put a reader in my pocket). It may not be worth the extra $50, but it does have a faster processor, so it may do better with the pdf Powerpoints slides. I just did somewhat of a compare and contrast here:
https://www.mobileread.com/forums/showthread.php?t=86531