Upgrade my70-210 3.5 - 4.5 USM

I’ve posted another topic, but I think I asked to many questions in one topic.

I use a 40D and I enjoy taking pictures of our dogs ( small black French Bulldogs) during our beach walks.
My old trusty and cheap 70 -210 3.5-4.5 USM really serves me well. Occasionally it wont focus at 200mm, don’t know what it is. But if I zoom back and forth the problem is solves.
Upgrade options;
70-200 f/4.0 IS as an upgrade, not too big, IS could be handy. But is the AF faster than the 70-210? When my dogs run at the beach I always struggle to keep them in focus.
135 f/2.0 also nice , less reach, but could be useful for other subjects , as I understand it works pretty well with an 1.4 extender.
100-400 f4.5-5.6 this is serious option as well. I would give me some more reach , it’s a pity that the minimum focus distance is 5.9' (1.8m) . Maybe it also handles less handy compared to a 70 -200 zoom lens. Bit worried about using the push –pull zoom also on the beach.

So these are my considerations. Appreciate your comments!

I don't have the 70-210 (nor have I used/seen one), but the 70-200 f/4 IS focuses VERY VERY VERY fast. I would think it would be fine focusing on your doggies.

The 100-400 is great if you want REACH, but it is a lot more difficult to handle/carry around. The push-pull is fine, but the 70-200 is much better for "casual" shooting and even works indoors well (if you have a flash/lighting). If I ever whipped out my 100-400 at a party, I'd be laughed at/kicked out of party. It is great for zoos/outdoor wildlife though.

Do what I did, buy both!

Okay problem solved, I'll buy them both ..... and find another place to sleep. Miss.Frogdog will not be pleased

I'm sure the 70-200 4.0 IS will focus at least as fast as my 70-210, I just hope somebody could tell me from experience with both lenses could say if this would be a major improvement.
If not I think I opt for either the 135 2.0 for the sweet bokeh. and keep my 70-210.

This may interest you:

https://photography-on-the.net/forum/showthre​ad.php?t=333670

My version of the 70-210 was pretty good. It sounds like the one you have is experiencing problems. The 70-200 f/4 lenses are a great step up. My non-IS version is one of my favorite lenses, one that I will likely keep for a VERY long time!

That's really helpful, thanks a lot!

I agree that it sounds like your lens may be having problems. The 70-210 and its big brother the 100-300 focus very fast (probably just as fast as the 70-200 Ls but without equivalent IQ).