Yes, I imagine both those boards would work for you, although going down to a 6'3 with lots of volume would feel a little strange and perhaps challenging at first. If you're determined to keep surfing and learning there is no reason why it wouldn't end up being a good board for you. A mini mal of that size would also be a good buy. You'll continue to learn a lot and if you can find one at a good price then a mini-mal is always a good investment. I am the same height and weight as you and after a couple of years surfing I'm down to riding boards under 6ft, however I really wish I'd kept my 7'4 mal for those tiny summer days when I want to go slide around on a few ripples, so no harm in buying one. I always say this to a lot of people when they are starting but in my opinion I think you should steer clear of 'pop outs' ie Bic's and NSP's and go for something that is shaped.
Go and have a look at some boards and think about their overall volume relative to what you are riding now, rather than getting too hung up on their exact length. Volume is important as it will get you into waves earlier and easier (you'll still need to work on your paddle fitness though). Find something you think you would be comfortable with but remember that you need a bit of a challenge if you want to progress.