QUOTE(yodanut @ Feb 25 2006, 11:51 PM)

Actually Xport, the slowdown doesn't occur all the time, only in certain (frequent) portions of the game. Encountering it for the first time in Metroid Zero Mission requires about 5-10 minutes of playtime: it's plainly noticeable when you reach the first brown vertical area in the game, in case you or anyone else wants to see what I'm referring to. Before then the game would run normally. According to the thread I linked to in my original post, other games, such as Duke Nukem Advance and Doom GBA, suffer from this issue as well, though I haven't tested any of them myself. I have no idea why it occurs, but it's definitely a bug in 1.7.2 and not related to the system's performance, since the emulator (including music) continues to run at 100%. It's only the gameplay that slows down.
I haven't performed the same tests you have, Xport, and perhaps the general relative performance of the emus does progress as you say under those conditions. All I've tested are the Metroid games during gameplay with no filters (i.e. Normal mode on PC, plain DirectDraw) and a frameskip of 2, and under those conditions 1.8.0b3 original stays full speed almost throughout the entirety of gameplay, even more consistently than 1.7.1 and certainly more so than 1.7.2. But perhaps this is only true only within certain games and scenarios and not overall. That kinda sucks for Metroid fans, but hey, what can you do? The interest and effort are appreciated anyway.
I don't believe I've experienced this slowdown of which you speak, but given the chatter on forums about it, I'll take it as a given that the problem exists. It really doesn't matter. If you were to load up Metroid in 1.7.2, get to the part with the slowdown, press the spacebar to throttle it, then do the same thing with 1.8, I'm sure you'll see that 1.8's max speed does not come close to 1.7.2. I understand that it's a timing issue and not related directly to how fast instructions are being carried out on the GBA emulation - but my point is that 1.8 makes *everything* slower. It may fix the problem with the timing, but that problem is hardly what I'd call pervasive. I can't claim to have played a lot of GBA games on XBoyAdvance, but my kids have and they can't recall ever coming across this problem. Furthermore, for the games that it does affect, it doesn't even affect most of the game - just portions.
Regardless, for the people who are really bothered by this, there is v19 for you. Someone will have to perform a lot more tweaking on the 1.8 core for it to be as fast as 1.7.2. As of right now, you can't have it both ways.