Yet another Second Board advice topic. Help!

Hi all. I've been using this site since I decided to take up surfing 2 seasons ago. I followed everyone's advice and bought a cheap used 7'4 funboard to start out on. I'm 6'1 and 180lbs. It was a bit of a challenge at first, but between last season and this one I've really improved my surfing. I can take off on and stand up on just abut any wave that comes through. I can turn down the face most of the time if it's not a closeout.
Last week the forecast showed some 4ft sets coming through, so I figured it was the time to go further improve myself by trying a couple bigger waves. Wow...it was next to impossible to get my funboard out to the lineup! I made it most of the way then took 3 or 4 right on my head and ended up washing back in to shore. I gave it another 2 tries...both with turtling and trying to duckdive (didn't work!). I ended up getting zero waves and went home frustrated...but not before watching some of the experienced guys duck right under those waves and make it out no sweat.
So now I've decided to get something a little smaller and more maneuverable. And hopefully something duckdiveable (I think I just made a new word).
There's a local shop that carries lots of used boards...but the biggest they have in stock is a 6'4 19 2 7/16 shortboard with a good bit of rocker. It's in decent shape and it's only $150. I'm debating picking that up and giving it a shot. I'd also keep my 7'4 for when it's small and mushy. I get out to surf at least 3 times a week...sometimes 4. Do you guys think it would be a step too far to try to take off a whole foot in length?
Or would I be better off with something like a 6'8 funboard that's 21 and 2 9/16? I can find one of those new for $300 with a leash bag and fins...but I'm worried that I'd run into the same problem of not being able to duckdive!
Sorry for the essay. And thanks in advance for your advice!
-Matt in Japan
Last week the forecast showed some 4ft sets coming through, so I figured it was the time to go further improve myself by trying a couple bigger waves. Wow...it was next to impossible to get my funboard out to the lineup! I made it most of the way then took 3 or 4 right on my head and ended up washing back in to shore. I gave it another 2 tries...both with turtling and trying to duckdive (didn't work!). I ended up getting zero waves and went home frustrated...but not before watching some of the experienced guys duck right under those waves and make it out no sweat.
So now I've decided to get something a little smaller and more maneuverable. And hopefully something duckdiveable (I think I just made a new word).
There's a local shop that carries lots of used boards...but the biggest they have in stock is a 6'4 19 2 7/16 shortboard with a good bit of rocker. It's in decent shape and it's only $150. I'm debating picking that up and giving it a shot. I'd also keep my 7'4 for when it's small and mushy. I get out to surf at least 3 times a week...sometimes 4. Do you guys think it would be a step too far to try to take off a whole foot in length?
Or would I be better off with something like a 6'8 funboard that's 21 and 2 9/16? I can find one of those new for $300 with a leash bag and fins...but I'm worried that I'd run into the same problem of not being able to duckdive!
Sorry for the essay. And thanks in advance for your advice!
-Matt in Japan