This is a very close fight, Namor is a hell of an adversary but I feel Hawkman will climb through early adversity and take the victory. I am going to show off some key areas that I feel will Win Hawkman this fight.
First off is durability:
http://static.comicvine.com/uploads/original/12/120679/3258643-justice+league+dark+(2011-)+023-002.jpg
Here is him tanking a hit from Wonder woman whom is possessed by pandoras box. Hawkman has also Tanked hits from Aquaman in the new 52 and Post crisis. I don't see Namor putting him down before he gets put down himself. Hawkmans healing factor and overall durability will play a large part in him staying in this fight and winning.
Speed:
Namor has not done too much in the way of speed, he has dodged an attack at over the speed of sound once but that is a really old feat. Namor did blitz wolverine before but Logan was not expecting it, still impressive yet I feel Hawkman still outclasses him in this area. Hawkman has a far larger array of speed feats than Namor and better feats as well.
http://i125.photobucket.com/albums/p68/DCHawks_photo/hm-37-02.jpg
http://i125.photobucket.com/albums/p68/DCHawks_photo/ShadowWarofHawkman01-05.jpg
http://i125.photobucket.com/albums/p68/DCHawks_photo/Hawkman04-04.jpg
Above are multiple scans of him dodging gun fire, it also shows just how reactive his wings are and superior flight will play a part in this battle as well.
http://i125.photobucket.com/albums/p68/DCHawks_photo/Identity_Crisis_02_Page_04.jpg
Hawkman's sight and reactions are so keen he can see wally west vibrating so fast he is invisible to everyone elses eyes.
Hawkman has done much more such as Dodging sniper bullets and more impressively fighting Lobo whom has shown to be on par with Supergirl in speed.
Strength/weaponry
I feel that Hawkman can finish Namor off, whether it be a mace of a cutting weapon Nth metal will prevail.
http://i125.photobucket.com/albums/p68/DCHawks_photo/hawkmanv217-04ocdhorus.jpg
Strong enough to lift up a solid steel radio tower.
http://i225.photobucket.com/albums/dd199/MachineMan616/JLAClassified48011.jpg
Here he hurts Wonder Woman bare handed.
http://i125.photobucket.com/albums/p68/DCHawks_photo/JLA70_VirtueVice.jpg
^knocks team busting desperos tooth out.
Fights:
I am not going to post any full fights but I will site a few, some key fights that I feel help secure the win are his fight againt Black Adam and Johnny quick. Black adam outclassed him in the end but Hawkman was able to stay in the fight, land some hits and tank some from teth. Hawkman was still standing after the encounter. Hawkman fought Johnny quick whom is a flash lvl speedster, they fought in pre crisis but the fight was also talked referenced in post crisis. Hawkman was able to land hits on the speedster and I feel this helps to show the speed advantage hawkman has over namor.
In the end it will be grit, equipment and speed that seal the deal for Hawkman. I don't see Namor putting him down.