OpenMSX runs a bit too slow

I think the MSX model you are emulating is not exactly same as the model you are now comparing it to. Games tend to work 20% faster on Japanese models when compared to European MSX models.

I think my original MSX is a 60Hz machine, since I ive in south america. My MSX machines were manufactured by Telematica in Argentina (Talent DPC-300 and TPC-310), based on Daewoo original designs.
The machine I use mostly on OpenMSX is "Boosted MSX2 EN", but I'm not sure if it is a 50hz or 60hz machine.

"Boosted MSX2 EN" is indeed a 50Hz ('european') machine. You can check this by using PRINT VDP(10) in basic: 0 means 60hz and 2 means 50hz.

So as already mentioned above, that's indeed the reason why it is a bit 'slower'. I know at least BlueMSX for sure also shows a difference, at least when the correct setting for the frequency is selected. It has the option to set a configuration to 50, 60 or automatic (so it could be that the default setting happens end to be 60 or automatic).

Luckily with an emulator you can just pick any configuration, so it's easy to pick another one which is on 60hz (for example "Boosted MSX2+ JP").

Indeed 'slower' and percentages are quite misleading ways to describe this problem... Computers displaying on 50Hz frame rate can actually execute 20% more code/frame... There are just 16.6% less frames. In real life only thing that changes is the screen update frequency, but in MSX game and music progress was typically tied very tightly to screen update speed unlike in modern computers.

There is also no "best default" as it depends a lot where you are coming from. Most of popular emulators originate today from Europe that was using mostly 50Hz TVs. On the other hand most of the best games and MSX standard it self originate from Japan that was using 60Hz TVs.

Let me try to open the problem a bit more: Typically when you run program designed for 60Hz on 50Hz it just runs 16.6% too slow. When you run program designed for 50Hz on 60Hz, it either runs 20% too fast or it starts to skip screen updates and in worst case drops to 60% of original speed due to lack of CPU time. Some games (on MSX2 and up) tend to force the screen update to some fixed selection regardless of the selected machine... or in best case the game may even compensate the music & stuff depending of screen update speed (typically a bit more modern games). In some games the 50Hz/60Hz selection does not really matter as the limiting FPS factor is the MSX CPU and not the screen draw. (maybe most typically 3D games and BASIC games) and some games / game loaders has a hot key, command line option or settings screen to select between 50Hz/60Hz (ie. disk cracks, ROM-loaders and such) On MSX1 the 50Hz/60Hz is fixed on hardware and the screen update speed can not be changed by software.

thanks, you guys!