I can't comment about the merits of a thicker rad vs an electric fan but what I will suggest as an absolute must if you go the electric route is as follows. There is a thread covering this but the search doesn't work currently.
a. Fit the largest diameter fan that will physically fit. This improves efficiency by sweeping the maximum surface area of the radiator and hence can spin slower (and quieter - this is important as you will find out). A single large fan covers a greater area and has a smaller void where the second motor would be. The model I got to fit was a
http://www.buhr-gmbh.de/en/products/engine-cooling-systems/spal/va18-ap51c-41s. and it was bloody tight ahead of the rad. Techinically, a "sucker" solution behind the rad is more efficient than the blower, but space is limited.
b. You need a quality brand with sealed bearings if you don't want to redo the job in 12 months time - the front of the car is exposed to dirty. often gritty water. Try an air-conditioner/refrigeration specialist if motor factors can't help you out.
c. Have the radiator modified to take a standard thermoswitch boss under the intake hose. Put this a little lower than ideal because the rad has no expansion tank as standard and the top inch or two is usually empty. This gives you the choice of loads of different switches. Avoid hacking hoses and sticking probes in the fins of the rad. It is cheaper (£20 in my case) and less likely to leak this way as well as being neat and unobtrusive. The thread is M22x1.5.
d. Whatever you do use a TWO speed solution. Any fan that blows with enough power to cover the extremes (i.e. towing a caravan uphill in traffic at 40 degrees) will be bloody noisy. You need a lower speed (simple resistor pack) to find a quieter level which covers 95% of the time. I used a 100W 0.45ohm resistor from ebay - about £3. Mine didn't need the high speed last summer even in 36 degree heat - but I'm glad it is there - this year I might try a higher resistor and lower the standard speed/power to reduce the load on the electrical system and make it quieter. Mine is a Peugeot thermoswitch 97-92 (high) and 93-88 (low) degrees. The temperature gauge doesn't go above 2/3rds up into the center "white" zone, 85-90 degrees I reckon. The high pressure cooling system won't boil until 122 degrees (higher depending on glycol concentration) but you really want to keep it under 100 degrees at most and stay around 90ish in regular use. Certainly I'm comfortable with fan fan kicking in at 93 being the normal operational "high".
I can't verify the claims of increased engine efficiency or warm up time using an electric only solution and there is one disadvantage - there is no flow at all in the engine bay when stopped. What would be ideal is if the fan always ran at a very low speed just to just move a little air around to avoid hot spots and build ups of hot air. This is essentially the P6s problem. The standard rad is fundamentally good in terms of capacity, the problem is the tightly packed engine bay. This is borne-out through experience with fuel vapourization and perhaps why they fitted the bonnet scoops on the NADA.