Well you will sell more cards with a fast core and limited fasram for sure but there always are people who want premium and will pay premium.
I would say start with affordable cards, feel the market and if there is enough interest AFTER the affordable cards are sold out then maybe make some premium cards, I for sure would buy a premium card for my A1200 but I will also buy the affordable card.
I will probably buy anything that you guys dish out for all Amigas I have

I am quite happy with my Vampire 600 at it is

Keep up the good work guys!