Caro 5...exf6

Viktor Korchnoi has played 5...exf6 many times (including his first world championship match with Anatoly Karpov), and this line has also been employed by Ulf Andersson. 

Black's 5...exf6 is regarded as sounder than 5...gxf6!? of the Bronstein-Larsen Variation and offers Black rapid development, though also ceding White the superior pawn structure and long-term prospects (Black has to be cautious that the d pawn is now a potential passed pawn in the endgame).

So yes, I would say that at the 2000+level, Black certainly still has winning chances.  It's way too early to say the position is that much better for White, so much so that Black is now playing for a draw.

Doesn't look very impressive does it?  I thought it was an interesting question so I looked it up on chessgames.com http://www.chessgames.com/perl/chess.pl?eco=B15&node=339109

Seems White wins: 37.6%
Black win: 18.2%
Draw: 44.1%

Although there are many not top level games in there of course.

I looked at 3 games where black wins, and all of them involved white blundering badly (or resigning in an equal game?  I guess the game score must be bad).

Seems like something to play for a draw to me.

Are there any books that recommend exf6 or at least mention it?

I have a copy of this book

http://www.amazon.com/The-Dynamic-Caro-Kann-Bronstein-Original/dp/0945806027

and I'm sure this book has a few chapters on both the exf6 and the gxf6 line.  However, unless your last name is Rockefeller, you're not gonna wanna pay the asking price.

Do you think it would be best used as a drawing line against higher rated players?

If you want to draw higher rated players and you yourself are not yet at least IM, then you should not play the CK-defense. Play some solid King-Pawn defense or some solid Sicilian like the Dragon or Pelikan.

In CK-defense, white will get so many completely different possibilities to play for imbalanced positions with in many lines even a minor edge.

- Advance Variation
- Panov-Attack
- 2-Knights-Variation
- occasionally the Fantasy-Variation
- maybe even BDG 

And even in the main lines just exchanging a pair of minor pieces and getting an open central file doesn't make it a safe draw. A strong player will always be able to create real problems for you in the late midgame or endgame and if you play only one inaccurate move in a simple enough position you are just dead on the spot.

Personally, I love the line 4)...Nd7 (to avoid doubled pawns) 5) Qe2 Ngf6?? 6) Nd6.  Shown that over 20 years ago and laughed myself silly.

4. ... Bf5 mainline is a safer option for black. 

I usually play 4...Bf5 anyway and I know all of the other options white has like the panov, fantasy etc..
This line seems pretty drawish to me black can just play c5 at the right moment and then blockade the passed d-pawn