To be frank, that's already banal, A big No NO if you expect others to keep to your rules. And, using caps and that exclamation mark in that "NO Banal Talk Pls!" statement sounds kinda rude too. You are asking for some advice, but it really sounds demanding. Perhaps you should try something like "Appreciate if I can get some nice advice", "Kindly appreciate if you lot can stick to the topic", "Appreciate if there are no off topic posts" etc etc :think:
Anyway, you demand for an answer, so let's try some serious discussion. Back to the topic, it's not playing fair to compare that 2 lens. The focal length, build, glasses, aperture are of 2 different class. If you really want a comparison, it only sounds logical to compare it with perhaps the "70-200mm f/2.8 EX APO HSM" or the "100-300mm f/4 EX APO IF HSM".
However, if you are thinking of upgrading, cos you need that extra length, then you should think of asking if there are some sites with test pictures, so that you can see the result yourself. Drop the idea of asking if you should upgrade, no one except yourself knows if you need that additional 100mm.
Personally, I'll prefer to try out the lenses, hold it, feel, it, test it in some camera shops, instead of visualising it.
Who the one who talk banal first? is YSlee not me.
Will you say thank you to YSlee after he slap you? Think about it.
Actually, I want to post it fast so I never look into the account that you guy will feel intruded after reading my post. I guess I would need to phase properly in future. Sorry if those who felt that my post is rude.
Dunno whether he shoot wild birds or not, but you can copy our resident bird king. Buy 500/4L IS USM, then stack 1.4x converter with 2x converter. And yes, after that there's still a focal length multiplier to tack on.