All the details you've provided sounds like the expected behavior for a stock PC card. What this means is you'll see nothing onscreen until the user environment loads. There does exist a procedure to add the neccessary EFI code to your cards ROM so it's properly initialized at boot. In effect you'll end up with a hybrid Mac card rendering full screen support at boot. Granted the success rate is highly dependent upon the card and how far it deviated from the reference design. In other words, the best way to insure a good flash is to get a PC card that's as close as possible to the specs of the Mac card you're trying to mimic. It's been years since I flashed my own card so I can't recall all the steps off hand but I do remember having to research which make and model of card to buy before flashing. I can't guarantee a prompt response due to it being Thanksgiving tomorrow but if you post your cards original ROM, the modified ROM you're currently using and the exact model of the card I'll have a look into rolling you a new ROM.
No worries - it works fine as it is - the boot screen is pretty unnecessary 99% of the time and now I have boot.efi working fine on Mavericks, I'm not too bothered about flashing it again. I've seen plenty of people who have flashed cards with no boot screen. The process you described sounds pretty similar to what I already did, so there's no guarantee it'll even fix it.