It's nice to see people still trying to get the most out of what they have! Not every 'upgrade' is an improvement.
It will help to know more about your PC's specs...assuming you can potentially install an older OS like 7 or even XP on that machine, you should be able to get even better performance (7 and XP also have better compatibility with earlier versions of MAME that 8 and later tend to choke on).
There are so many ways to approach this, but my immediate suggestion (since you mention input lag being an issue) is to consider going back to a version between 0.99 and 0.106.
These are both milestone versions for different reasons.
0.99 is the first version that runs Robotron at the correct speed (earlier versions ran it too fast), supports all of the 90s Golden Tee games, still supports hiscore.dat, and all of the 'golden age' games were by then emulated nearly flawlessly (unless you're a MAME developer and well schooled on the hardware, or a veteran player who understands the quirks of certain games, you will notice virtually no differences from the actual machines).
It is also notable for having less input lag than later versions, which is one reason why some STG players still keep it around; in fact, 0.99 was forked to create ShmupMAME because of this, though they re-forked later on.
Various changes were made after 0.99, with 0.106 ultimately being the final major version released to still have the old video code...the minimum hardware requirements shot way up with 0.107 thanks to a significant rewrite of the code, which is why many people have held onto (and still recommend) 0.106 for older PCs.
Since you specifically mentioned Pac-Man, then for what it's worth, three of the five highest MARP scores on the parent "puckman" ROM set (including a perfect 3,333,360-point game) were set using WolfMAME 0.106 (
http://replay.marpirc.net/r/puckman).
In general, you can take your pick of any version between 0.99 and 0.106, and you should get good results.
If you're REALLY feeling like a rebel, you can go further back in time and take a more vintage version of MAME.
A lot of it comes down to your personal preferences, but I have come to find that 0.62 is an exceptionally good release.
This version is notable for a lot of improvements, including improved raster effects in CPS2 games and sound fixes in Neo-Geo games (including the KoF '99 "How to Play" screen and the Shock Troopers attract mode).
Basically, 0.62 is the first version with which you can play all of the CPS1, CPS2 and Neo-Geo titles supported back then without any noticeable graphical, game-play, or sound-related issues.
This version is also old enough to still have a lot of speed hacks that were taken out of later MAME versions, resulting in performance gains for many games...even on modest hardware, everything I've tried runs at full speed, without so much as a single dropped frame (including the Mortal Kombats & other 90s Midway games).
No important games seem to be broken in this release, either.
ROM sets for old MAME versions can be found if you know where to look, and ClrMAMEPro also comes in handy for converting modern ROMs to work in the older versions again (it can be a PITA, though).
0.78 is a version for which ROM sets can be easily found, so this one is also worth taking a look at (some of the speed hacks were starting to be removed by then, though).
I hope some of this information may be useful to someone!
It's nice to post here for the first time...I've read threads here for years, but haven't posted anything until now.
I figured it was better to share my thoughts here rather than bump an ancient thread from over half a decade ago...I've spent quite a bit of time trying different MAME versions out, and with a lot of trial and error I can say for sure that 0.106 and earlier are your best bets if you value fast, reliable performance above everything else.
Best wishes to everyone!
T.L.D.R. - a version between 0.99 and 0.106 will allow you to run the most games with the least amount of input lag, while still having good performance on modest hardware thanks to the old video code; even older versions of MAME should give you more speed, but you will be missing out on emulation improvements made since then.