I would enable it unless it's causing a conflict. Believe the interrupt is generated on vertical refresh.

I think it causes a conflict with my VLB I/O controller... floppies are dead and I see erratic graphics behavior... I can bother fixing this (will need some help though) but first I want to know if vga_irq on such a system makes a difference 😀

Read this:

http://queststudios.com/smf/index.php?topic=1788.0;wap2

The explanation was new to me, but experience with Cirrus and other cards supporting IRQ2/9 had already shown me that it can be safely disabled without losing compatibility with games.

Ditching the IRQ for the VGA will slow it down in use for fast vga graphics though.

From the top of my head, the only game that needs the IRQ enabled is the EGA version of Gauntlet, but that one still wouldn't work correctly on any VGA card (for a different reason).

just an update:

I removed both the vlb 5428 and the i/o controller , they seem to have issues on this build.
I am using a different vga now, a vlb 5424 based one that had the IRQ jumper to ON by default and an ISA i/o card (don't have any more vlb ones...)
Things seem to run fine , I believe that the vlb i/o card was faulty. The 5428 card had crap quality...
Thanks for the help!

According to the manual that came with my Viper VLB card, the IRQ jumper is a compatibility setting for EGA software that requires its functionality. VGA operations normally don't use an IRQ and cards with the jumper usually leave it disabled by default.