Wieser buddy,look at your post,you tested at 12 yet in FSO you were at 20.5K!
I assume you are talking about indicated speed and the true speed is what you need to watch!
The arena settings are slightly different,the TA has damage reduced to a minimal amount,basically 1000 bullets equals 1 bullet but that is the only difference. In the SEA they may have a couple things setup,killshooter off,wind,etc. but none of these things effect A/C performance.
As for the lag spike you saw,well it could have been on your end or on the enemies end,either way that's an internet issue and AH can do nothing to fix it.
If you want to find out who has the connection issue,open clipboard map,right click and select net status,look at top graph,varience and delay,if you have the problem it will show a saw tooth "spike" if it's a nice flat line then the other guy has the issue.
Hope that answers things for you,come look me up in the TA if you wish to discuss this further.