What should I do? =(

I was in a pub with a... very highly ranked person, and while I'm not 100% sure, I think that he might have been using a 1 hit kill hack. I'm not a noob that thinks everyone hacks, trust me on this, but several times he killed me from 50-70+ health with what looks like only one non-headshot hit with an M4-C. It could just be a few shots all lagged together a few times (his ping was ~150) but when I watched the replay it looked very probable that he was hacking. (Targets died on what looks like the first shot, but several shots after it make it hard to be sure. I know that hackers sometimes fire a lot of bullets at a time so it makes it harder to be spotted and/or banned) I have an Xfire vid of the game but he only killed me about 3 times in it, and his K/D wasn't completely insane, but I still think he might have been hacking. He also wasn't getting hardly any headshots but still managed a high K/D. He has spent a LOT of time on his account and I don't want him to have to start all over if he just lagged a little so it looked like he was hacking, but I can't just let someone of this rank actually hack and get away with it. Should I send in a report and possibly have someone that worked hard getting their account where it is now legally banned, or not send it in and possibly let a very high ranked hacker continue to kill people and call it skill? I can upload the replay/Xfire vid to Youtube if you want to check it out for yourself.