Rigging: How fast is it onshore?
I can't say there is a big difference in rigging. It is different, but hard to point out which one is easier? The Overdrive has rollercambers which makes it less sensitive for camber/batten pressure and rotation performance. The Reflex has 1 more camber. I think the reflex is rigged a bit faster by me, but just because I am used to it.

Tuning: Do you need a guide?
Overdrive... Much easier. Put maximum tension on bottom 2 battens, medium tension on middle 2 battens and no tension on top battens. The reflex 4 is the same idea, but the reflex has a smaller tuning range. So downhaul should be good in a range of 5mm where the overdrive works in a range twice as big. Same with outhaul, battentension, tackstrap, etc...

Durability: Which one will last longer?
This is difficult, since I have the sails only for a short period. My experience is the reflex can do at least 50 sessions without any loss of performance, the overdrive has yet to prove itself for me. When using it normal the sails are good for many years for a weekendracer. The overdrive is lighter and the reflex seems to have a bit more expensive materials. My feeling the Reflex will last a bit longer, but not by a big difference because the construction method is almost equal.

On the water: The feeling is what really matters
To my surprise there is a small difference over the whole windrange between both sails. So when sailing the overdrive in the sweetspot it is a slightly different feeling compared to the reflex. In short:

Overdrive:

• Gives more feedback, preventing oversheeting the sail continuous. It is much easier downwind
• More powerful for its size and lighter, you will be earlier away. Or you can sail smaller with a much lighter sail using a smaller board 
• Stiffer profile and leech, the overdrive is not a floppy sail. I use a 460 blueline in 8.6 (490 is rec.) which is OK. The Enigma 430 in my 6.2 is giving a stiff profile (for lighter weight speedsurfers I would recommend RDM or a shorter SDM)
• Easier rotation 

Reflex:

• More stability in highwind, in strong gusts the sail opens and gives the rider range, if willing to tune it and willing to sail big (for example 7.0 in 30kn+). My feeling is the difference it not the construction, but more the hours of development per sail, reflex is just developed to a very high standard with enigma mast
• It is possible to increase lift very quickly by outhaul,
• Upwind performance

Speedtalk: numbers
I know this is speedsurfingblog, so the numbers on the gps are one important parameter to be considered. In many conditions the Overdrive will not disappoint you, eventually the reflex will be faster in each size but I think when you just take a smaller Overdrive you will be competitive. I did not do yet a fast session this year, my 2013 bests:

• Overdrive R4 6.2: 66,33km/h average + 69,84km/h topspeed
• Overdrive R4 6.2: 64,39km/h average + 68,33km/h topspeed
• Overdrive R4 8.6: 58 km/h average + 61,33km/h  topspeed
• Reflex 4 7.0:  65,46km/h average + 68,71km/h topspeed

Concluding
Reflex is faster when you are willing to sail powerfull and know what to do without feedback of the sail, the difference is estimated <1km/h up till +- 80km/h boardspeed. I believe the Overdrive is faster when you don't have the big muscles and don't know exactly how to push the sail in the right angle at any time. For me it took a few good hours to tune the Reflex, and a few minutes for the Overdrive.