Most media players I owned, had some issues with odd brand cards.
Generally Sandisk is one of the most known, most stable, and most compatible with all devices.
I personally would believe that 32GB is currently the limit of cards, but I'm more familiar with the x86 architecture world, where this limitation has to do with how you format the card.
I know one thing, you probably will experience problems trying to format the card in COMPRESSED NTFS. But I guess cards will be either formatted in FAT32 (in which your limitation may lie between 4,8, 16,or 32GB top), or any of the ext formats.
Many hardware states a maximum of 4GB, but then over time proves it can run a 16 or even 32GB card just fine.
As far as speed factors,I never really came across a media player (because I have currently nothing else to compare it to than a ARM based media players), that could not read a card because it was 'too fast'. I did come across some cards that did not work, most likely because of the combination of SD manufacturer, speed rating, and the device's card reader; there might be an incompatibility in speed settings;but those are generally oddballs.
I also see no reason why a 128GB sd card would not work, as long as your card reader supports it. If it's connected via USB, then it'll depend on the card reader.
If the device had an internal card reader, it might be more of an issue.