Mid tele for Wildlife, 70-200mm F4 L IS?

I'm looking for a lens that I can use as a walk around wildlife lens with my 7D, mostly for gulls, squirrels or any other wildlife I need to zoom back for. I already have a 300mm F4 L IS, and 400mm F5.6 L for my general bird photography I do on a regular basis, so something in the 70-300mm range would be ideal. I've used plenty of lenses in the past but not since I've got fully into wildlife photography, it's given me a view at what might be worth getting. I need a fairly good focal length and fast AF for the wildlife I take, and would like to use the lens for Birds in flight too.
Just a note I already own a 1.4x TC Mk2.

Here's my thoughts so far:

Canon 70-200mm F4 L - Owned in the past when I had a 40D, Great IQ, worked well with the 1.4x tc but don't remember how fast the AF speed was with it on ( might be able to try it in jessops tomorrow). Found it difficult to handheld without IS but I can handhold the 400mm F5.6 so it might not be an issue now but would still prefer the IS version it's just a lot more.

Canon 70-200mm F4 L IS - has a great reputation, Very sharp, IS is 4 stop, AF very fast, Im sure it wouldn't be bad with the 1.4x ( anyone got one with an opinion on it?).

Canon 70-300mm IS - Owned before, would have still had it to use now but my mum broke it while using it, build quality not up to much, IQ not bad but could be better.

Canon 70 - 300mm L IS - Heard mixed things so far, AF pretty fast, IQ Good but heard mixed results, IS good, Heavy for what it is, Very expensive for what it offers.

Canon 100- 400mm L IS - Great lens, Best stopped down at 400mm though, best range, would work as a main wildlife lens at times probably better to use than my non IS 400mm F5.6 in a walk about situation. Heavy for a walk about lens though and push pull system not to my liking.

Canon EF-s 55 - 250mm IS - Have owned it and my dad owns it now, Great bang for the buck, AF Speed lets it down for my needs, I remember continuous speed not amazing.

Tamron 70 -300mm VC USD - Tried it in the shop, pretty sharp, but AF not perfect, speed was ok but would rather get a 70-200mm F4 non IS for the price of this lens.

So As you can see Im stuck! If anyone can help answer some of my questions and offer a suggestion it would be greatly appreciated, Thanks.

Birds, wildlife? 400mm is just a begining.

you have a 300mm and 400mm...what range are you looking to cover? I'm not sure how 70-200mm would be any helpful, unless we're talking about zoo animals.

For what you're describing, and the lenses you already have, I suppose I'd lean toward either the Canon L or Tamron 70-300. While the 70-200s are great lenses, the chances that you have for getting close enough to the critters in that range seem quite slim.

If you're up for a zoom for that, I will always recommend the 100-400. That thing's been champ for me; others have done remarkable things with the Sigma 50-500/150-500 lenses, as well.

You could sell all the lenses you have(300 and 400) and get a 300 2.8 IS. It'd take a tele pretty easily!

Sell your 300 and 400 and get a 100-400. Covers everything in a nice, relatively compact, package.

Look at a Tamron 18-270 there are two versions and both have come right down in price recently. The new one is very compact. I have the older one and it has served me very well for the last year and a half as my main lens. Some good shots in sample section.

Cheers for the info so far. I should have made it clearer what my intended use for the lens was. Basically a general purpose tele zoom, something for tame wildlife, Ducks, Gulls, Pigeons, squirrels ect. Also for anything else that takes my fancy for example when I'm by the coast on holiday or when Im at a Zoo. I have my wildlife lenses which do me just fine, though I'd always want longer.

A 300mm F2.8 would be nice but even if I sold what I had I couldn't afford one, least not here in the UK.

I'll try out the 70-200mm F4 L with the extender today in the shop and see what I think before making a decision.

100 400. I love this lens. It is not too heavy so you can walk around with it all day and the IQ is great. Only drawback is that it needs a lot of light. Its OK for walking in the forest if you have a very stationary subject. No good for birds etc in this situation

I took mine out for a walk last week as I didn't have the 500 with me. Managed to get some pretty good deer shots in very bad light but they were very still and I was on a very sturdy tripod

This was at 400mm, 1/60s, f5.6, ISO2000

IMAGE LINK: http://www.flickr.com …/56355379@N03/5​597436371/