Regarding netcode I must say its greatly improved, even in large crashes I noticed cars not warp around anywhere near as much as they were in the past. With solid connection people its been very stable since the latest patch, still guys that are a bit up and down ping wise issues happen but even amongst the league guys not too many have been having big spikes around me.
Running 64bit now has replay fixed so it will record 1GB assuming you have enough free Ram, probably not recommended for guys running on 4GB systems but people with 8GB or more should easily be able to get larger replays. I don't know why really there needs to be a limit as for example I have 32GB of ram and it should be able to use much more. The other thing is that I don't know why replays are so large in the first place plus I think replay quality levels going by the ini files is this.
[QUALITY]
LEVEL=4 ; 0=~7Hz , 1=~10Hz, 2=~15Hz 3=~30Hz 4=~60Hz
So not sure what the server hz rate is on the race server but I assume 20hz as default, Ive dropped my servers down to 15hz as bandwidth was getting a little high at times and this just drops the extra cost per month with no real noticeable quality loss now. 3rd quality level saves at 15hz and 4th at 30hz, the only difference you will noticed there is your car will be smoother at Ultra but all other cars will be pretty much as you see them from the mid setting up.