What's your budget?
Not sure what you mean by shutter lag... I've never had a problem with any of my Canon DSLRs. Though I'm a pretty average photographer.
Craig and I both use one of the older model 7D's, and they're unreal (and about a third of the price). I'd highly recommend it.
imaging-resource.com is a good site to check out the specs (and reviews). The shutter lags for each camera can be found under "Performance" heading of each review.
Plenty of options other than what you were considering for less cost.
My missus has the Canon 1300D with 400mm lens and she loves it. Bit cheaper but well adequate for amateur hour. I’ve taken the odd surf photo here and there with it and never found shutter lag to be an issue.
You preset the auto focus well in advance of taking a photo. Once you’ve picked your target just a semi tap on the shutter button and range is established. This remains set till you restablish it at another distance.
@blindboy, 7D mk ii , with a smaller sensor, will give you better reach with a 400 mm zoom than a 5d mk Iv (saw them on special for under 3k last month so don't pay $3700 if you go 5d), similar to a 600 equivalent on the larger sensor. Shutter lag is unlikely to be an issue if you shoot with high speed burst rate of the 7d ( 10 fps?) or pre focus as per Blowin. Full frame sensor (5d) gives you more to play with when cropping images as well as improved dynamic range, colour depth and resolution. I run a 5d mk iii and older 7d and love both. You can't go wrong with either but buy the canon L lenses.
I have a 7D Mk1 which I have been using to shoot rodeo over the years and it has never failed to deliver. The 7D series are consider the "Sports" camera as they shoot more frames faster than a 5D. The smaller sensor camera's do generate quite a bit of noise at higher iso settings so once you go over 400 expect to have to do some work in processing to rectify that.
These were shot with a 7D Mk1 and a Canon 28-135 zoom IS lens @iso 400 so effective focal length was 1.6 times 58mm in sports mode with custom white balance and AI focusing enabled.
I would think the mk2 7D had major improvements to the hardware to reduce the noise issues of the first version. What I do recommend is finding a camera and lens hire joint and hire one for a weekend with your lens of choice and go shoot some frames. Hire a Nikon as well and try that out. I have not been overly impressed with my canon glass as I am seeing much better results from Nikon and third party lenses of late. Don't discount paying much less for a tele by using a third party lens like a Tamron, some of their lenses really do deliver for the price.
If you have any other questions feel free to ask.
I asked my brother for you about this BB. He’s been a professional magazine photographer for around 30 years, and they swear by Canon. He said that even with their really good cameras, in low light that auto focus thing can be an issue. Pre focus as mentioned, gets around it. He also said that there is one piece of advice he would offer; you know how I have my focus button on the "star button" on the back of my Canon? Most of us chose to use that custom function, so we don't have to half press the shutter button to focus. So much better control having focus control seperate from actually pushing the shutter button! And also from my brother; And i think he needs to get that 100-400mm telephoto lens! That's the one he really wants! He doesn't need to "master" the standard zoom lens first...
Hi BB what did you end up buying? I despise Cann for continually changing their lens mounts, unlike Nikon who kept the faithful old lenses usable even if they are not perfect on digital bodies. The worls is full of unnecessarily obsolete junk thanks to Cann et al. I loathe their flippant changes. I use a Nikkor 500 F4P on older digital FX Nikons and the results are superb. I wouldn't waste money on a zoom that covers 100-400 as the 100-300 range is useless for surfing I reckon. Go hard or go home is the key to success in sports photography. Pretty much any half decent body is good enough, it is the lens that makes or breaks the image. but you are right to be concerned with shutter lag - for any sort of photography that is a huge help to have the minimum possible.