Trying to figure out if the system is 34 gallons, as originally stated, or 49 gallons, as it would be from originally stated dimensions, a difference of almost 50% is a clarification and not being a pedant.
I like Sicce pumps... quiet.....
Look at this one.... it has max head of 6 feet... how many feet are you pumping up, I am guessing 5 ?? So this one would work..
http://www.bulkreefsupply.com/sicce-syncra-silent-1-5-pump-357-gph.html
You can look at Sicce site, and it will show you how much pump will move at various heads
http://sicceus.com/aquarium.html
If you are pumping to 1.5 meters or so, this shows the 1.5 will move about 120 gallons/hr and the 2.0 will move about 240.... again, at 5 feet head. These pumps are also adjustable flow, so you can get less flow.
How much flow do you need from this pump vs. running additional power heads in the tank. I have a 125 gal/hr pump in my Innovation 40 gallon, and an MT10 power head as well, and that is plenty of movement.
There is no singular answer to this question. I think the Sicce 2.0 would provide the proper flow if you throttle it back quite a bit, and if you are using the return pump for a significant amount of your flow. I would pick the 1.5... because I have a power power head in my tank as well.
Other considerations... the bigger the pump, the more the water level goes up in your tank... the bigger the pump, the LOWER the residence time in any media the water is passing through, although it should pass through more times, so that may be a moot point.