Your case supports 140mm fans just fine and i don't see a reason why you shouldn't go with AER140 RGB over AER120 RGB. Unless if it comes down to a price. Though, 140mm fan advantages over 120mm fan are more airflow with less noise.
As far as 120mm fans go, AER120 RGB fan is still better in airflow than Riing 12 and it's 2 versions.
Airflow specs:
52.44 CFM - NZXT AER120 RGB
48.79 CFM - Thermaltake Riing 12 TT Premium
40.6 CFM - Thermaltake Riing 12
Static pressure specs:
2.01 mmH2O - Thermaltake Riing 12
1.35 mmH2O - NZXT AER120 RGB
1.11 mmH2O - Thermaltake Riing 12 TT Premium
Thermaltake Riing 12:
http://www.thermaltake.com/microsite/Riing12RGB/index.html
Thermaltake Riing 12 TT Premium:
http://www.thermaltake.com/MICROSITE/Riing12RGBRadiatorFanTTPremiumEdition/index.html
As far as fan wires go, they should reach. I have 2x full-tower ATX cases in use where my HUE+ is at the front bottom of the case while my AER140 RGB fans are at the top of the case. All my fan cables reach just fine.
Though, your H500P is one of the worst cases when it comes to the airflow and here, i'm not sure if even AER140 RGB fans would be enough for proper airflow. What H500P has, is good looks and that's it. Airflow, build quality and materials used are all sub-par. If i'd have to use that case, i wouldn't look anything below Noctua industrial 3000 RPM fans (
specs). But if even Noctua wouldn't cut it, i'd go with Delta industrial 5000+ RPM fans (
specs).