Getting out back without having to duckdive too much etc. involves one of the hardest elements of surfing - when you arrive at the beach, don't paddle straight out.
Take 10-20 minutes out to watch the waves, you should be able to establish from this how many waves are in a set and how long the lull between sets is.
What you then need to do is walk out to your depth and wait - jump/ duck under the waves until the end of a set, then get on your board and paddle like crazy to get out before the next set comes in.
As for duckdiving a 7'5 board - yes you can. I duckdive my 7'5 mini-mal easily - my friend can duckdive his 9'6 longboard. The thing is it's all about technique. If you try and push straight down on a buoyant board it's going to be hard. Try this:
Paddle at the approaching wave at a slight angle. As it approaches, push down on one rail, to get it under the water, then shift your weight to the other hand and the board will be under, the rest of the duckdive is as normal.
Hope this helps