I seems to remember GTA Vice City doesn't require any MODE from other devices, so it could be a SMB only problem, but most probably there's some relation.
Try the game from USB if you want to check the compatibility (GTA games plays the same from any device being streamed by little chunks of data).
I've always just assumed that at least modes 3+6 were necessary because of reports of freezes during gameplay, but you're right, the game boots up just fine with no mode enabled at all. I just didn't test it myself with these two modes disabled for longer periods of gameplay, since I've never had an issue with those enabled in the first place.
As for mode 2 though, the game always had the studder issue for me when this was not enabled. I also think this is a game specific issue and not an SMB speed related one since games work fine for me with Mode 2 enabled or disabled corresponding to compatibility lists. I tested with SCPH-70001 (which tends to be slower over SMB because of the remaining MIPS R3000 processor as I learned
here, but the latest OPL versions seem to work a lot better, so OPL might have already been optimized for this specific model) and an SCPH-77004.
For now, I just keep the working OPL build around and start this one up if I want to play the game smoothly with Mode 2 enabled. But of course, it's nice to aim for an all-in-one solution, where such an issue is resolved if possible
As for GTA Vice City through SMB what about mode 1 (or 1+3+6)?
However something is differently not right if mode 2 has started to block this game from loading
while everything was fine in older builds with it...
Sorry, I didn't post that I've already worked through the relevant, different mode combinations. I've tested with Mode 1 only and Mode 1+3+6 and the game boots up fine with these enabled, but the studder issue unfortunately always remains for me and only disappears with Mode 2 enabled in the old build.
As a matter of fact, the Mode 2 loading issue seems to affect the other two games of the trilogy as well. GTA III and San Andreas both hang on the title screen with it enabled but I didn't test it as deep as Vice City. So I can't say for sure if those two also stopped working with the build mentioned in my previous post or even earlier/later.
I wanted to share this with you guys since you have the insight and might figure out, what goes wrong here, so I try to be as specific as possible.