Good thinking and perfectly logical reasons. I think you're doing the right thing. The ET70 feels noticeably more compact and is for me (70kg) simply a better fit. As you, I almost exclusively rode the ET74 since I got it and was super impressed by its versatility and range. Almost to the point that I was worried to get the ET70: I like very much to have boards with that all round quality and thought that maybe the 70 would be better for most conditions but would still loose out on all roundedness.
But in fact, the 70 is maybe even more all round for me and I only sailed the 74 once (for pure comparison reasons) since I got the 70. Even underpowered conditions is very nice on the 70 (as long as you don't need the float of a significantly bigger board).
Anyway, good luck with the board. I hope you're weekend goes off.