There's no downside. The more people die from excessive speed the less people on the road during rush hour traffic ;)

Pssshhht! Like I could even go that fast half the time anyway. Its bumper to bumper around here when I'm commuting.

Most fatal crashes happen at intersections and crowded roadways, not the interstate. In certain situations, faster is better. If you are slow than most traffic, you hold up a lot of people causing congested roadways and in turn, causing wrecks.

Whenever I drive automatic, it's a pain to drive at 65, over time I slowly speed up to 70 and it drives me crazy. I can't just drive 65!

As long as people understood how to drive; I.e. What lane to be in, there shouldn't be a need for any speed limits.

Look into the autobahn for your research project.

Ultimately, it does depend upon what consequences you value more: safety, efficiency, liberty, etc. The research is conflicting and generally biased in its presentation, and if I am honest I do not care enough to dig past all the superficial misinformation (e.g. like this and this).

If we are strictly discussing raising the speed limit from 60/65 to 70MPH, however, I would contend that the shift in harms and benefits is fairly negligible. Collisions are likely to be critical or fatal traveling at 70MPH, but the same must really be said for 60/65. The incidence of accidents might go up, but I do not have the evidence to know one way or another and rather doubt that 5-10MPH makes much of a difference; accidents are usually caused by negligence above all else and negligent drivers will be negligent regardless of the limit. As far as efficiency goes, a change in 5-10MPH is also not terribly significant unless you are traveling distances more efficiently covered by other means of transportation (e.g. train, plane, etc.).