How big current I can commutate using D-sub connectors?
Have a datasheet: http://portal.fciconnect.com/Comergent//fci/drawing/c-dsub-0071.pdf for http://www.digikey.com/product-detail/en/865609SLTLF/609-1467-ND/1001781 which claims a max of 5A per contact!

Personally your 45A total seems like a horrifyingly high number, but if you wanted to split your 10A across 10 power and 10 ground connections in a 25 way connector that seems OK. 

Don't forget the wire gague; http://www.powerstream.com/Wire_Size.htm says 20 AWG or larger (smaller AWG number), but it also needs to fit the D connector.