The issue with with your pipe being all the way down in the sump and hitting a filter pad is that pad is going to get dirty very fast and you will have to empty that entire left chamber to get to it and clean it. To me, that would be a lot of work that I wouldn't want to do every 1-3 weeks..depending on how fast it gets dirty. If you have it go from the top, you can change the filter pad very fast and easy without taking up much time. There is a reason that you see most designs pretty close to the same, years and years of others experiementing has made it easier for us today 
As the old saying goes, "if it isn't broke, don't fix it." You will be glad that you went with an easier setup when it comes to maintenance.
The 55 is not overkill for your tank....I would infact do a 100 on that size tank, but the 55 will work. Just ensure you leave enough room in your wet/dry to catch the overflow from the tank on a power outage.
As the old saying goes, "if it isn't broke, don't fix it." You will be glad that you went with an easier setup when it comes to maintenance. The 55 is not overkill for your tank....I would infact do a 100 on that size tank, but the 55 will work. Just ensure you leave enough room in your wet/dry to catch the overflow from the tank on a power outage.
