I keep fastest lap replays.
Always.
My main tuning track is Apricot, I have saved 4 or 5 best replays for each; 450pp, 500pp, 550pp, and 600pp
They all roam around the same 2 second window so it's easy to tell which is which. It also keeps track of what my current fastest cars are for each pp level. All good things.
Do you setup up offline, then go online? there is slightly less grip online, for me its about a second per lap
Continuing from above, elaborating the online issue;
Yes, offline.
But, once you know what you need to alter to make a tune good for online, it can easily be done for any tune. It is kind of driver specific what those changes are, but it shouldn't take very much play to see what works for you.
Some use a +1/+1 higher brake setting, or reverse. Some add 3 or 4 points to braking lsd setting. Some don't do anything at all and just drive more careful.
I like to test online a few times during the process, just to see differences if they are noticeable. But I rarely change my tune just for online play, rather tune it to work good and test good on both. I also am not an elite master tuner from the God's either, so this is just one more thing to consider, lol ^^