Surfing Waves

I apologies already for another what surfboard to choose question but I couldn't really find the answer online.
I am looking for a board with less volume than my fish I normally ride and I am visiting my local shaper Spider who have been super nice and helpful in swapping boards around for me to test.
I am trying to get a used board from them so of course they can only give me what stock they have.
I tried a 6.0 30ltr performance board with an aggressive concave / rocker that was far too advanced for me so I took it back.
They gave me a different model 5'8 28.4ltr which I thought no way its too small but I tested it anyway and it was so much easier to paddle and get into waves than the performance board, this is because it has a more weight at the front and not a radical concave.
I only tested it in crapy tiny conditions yesterday so will try it again today but 5'8 sounds small for me, I am 5'9 and weigh around 70kg, what are the disadvantages with going for a shorter board? will it slip out on bigger waves compared to a 6.0?
Thanks for the advice.

So much more consider than size, fins profile and as you found out where the volume is distributed.
If you have Spider advising you , familiarize him with what you are doing in your surfing and what you want to develop.

Super aggressive features , conclaves etc. require a high level of skill to utilize them.
Talk to your local surfing crew and see what they use.
If there are guys around your level and similar in size, see what is helping them improve!

You say it is easier to paddle into waves but what happens after you catch the wave? How does it ride? Changing the fin size can help to adjust the board for different sized waves. The actual design will also affect how it handles bigger waves as well as your skill will affect how it handles bigger waves.

"Too many cooks, spoil the pot". If you are already being advised by those at Spider, listen to them and give honest input to their questions. They know you and their own boards better than any of us.

Cheers for the replies guys, it was nice to test the different boards to know there is so much more to choosing a board then volume and dimensions.
Fins is something I never thought about actually.