MKI upto MKII lens upgrades

Have now upgraded many of my smaller lenses from the MKI version upto the MKII versions and do notice the difference in the 70-200 and 100-400 but am also now looking at getting a larger prime again but am stuck between getting two of the MKI series primes second hand over a new MKII.

Have owned the 300 f2.8 IS L and 400 f2.8 IS L and the image quality was superb but the weight of the 400 was beyond carrying it around a racetrack shooting superbikes for a weekend.Know i am aware of the massive weight reduction of the 400 but i am either looking at getting a 300 f2.8 IS L and 500 f4 IS L second hand as a pair or just going all out for the 500 f4 IS L MKII to attach onto a 1DX or 7D MKII mainly but with the odd occasion of also using it on the 5DSR.

So has anyone moved upto the newer MKII large primes from the MKI's and was there a major gain in image quality and A/F performance bare and with the 1.4 tc MKIII attached?

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Two major points to consider:
1: The version 1 discontinued lenses will, sooner or later, not be serviced by Canon anymore. . The time is drawing near for many of them.
2: The Image Stabilization on the older lenses is only good for about 1 1/2 stops, while all of the version 2 supertelephotos feature IS that is good for 4 stops.

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Gadget-Guy wrote in post #17822280
........... i am either looking at getting a 300 f2.8 IS L and 500 f4 IS L second hand as a pair or just going all out for the 500 f4 IS L MKII

It seems like you might be a perfect candidate for the 200-400/560 f4.
Have you considered this lens for your motorsport needs?
Surely you wouldn't be carrying both the 300 and the 500 around the track at the same time, so you would pretty much be limited to how you could frame images at any given time. . It seems that the big, albeit hand-holdable, zoom would be most useful for these situations.

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Cheers Tom,

Didnt really think about the service life span of the older lenses in all honesty.

Have tried the 200-400 with built in converter and didnt like the weight or the image quality in all honesty.

Have the 100-400 for carrying around on race day attached on the 7D MKII along with a 70-200 on the 1DX for for pit work and swapping this over for the 24-70 on grid.

Looks like i will more than likely go all out on the 500MKII in all honesty as even the 400 f2.8 IS L MKII i feel would struggle with the 2x tc at some of the bigger circuits compared to the 500 f4 IS L MKII with the 1.4 tc.

Must see if i can borrow one for a try before next season from Canon CPS.