1. Yes!
2. 70 ns or 60 ns are typical speeds
3. Only one way of finding out 😀
4. Western Digital, Tseng ET4000 and later Cirrus Logic are all fast.

Is 60NS actually any faster?
WD made video cards? waaaat

60ns isn't faster by itself, but you can set motherboard operating speed higher and/or dram latency faster (but sometimes 60ns doesn't provide anything more than 70ns couldn't handle - test is the only way to know for sure).

Beware of early ISA video cards that are really only suitable for slow 386 and 286 and older systems. I have a few of these as they work in an XT motherboard, but are slow as hell in anything new.
Doom is unplayable with these cards due to only 10fps as opposed to over 25 with faster cards.

High end ET4000, Cirrus logic, and others. I strongly suggest You watch some of Phil's Youtube videos.

Running a Dx2-66 in a non-Dx2 system, might make it post. Though you will only run it as an Dx-33.

And as others are saying, go for something late-era gfx card. On the ISA types, you can not really go
wrong on the ET4000 ones.
Cirrus Logic cards that are ISA only, I really do not know what exact card you need, as I have no benchmark
numbers from those type of cards. I suspect that something like 5424/28 will do fine too.
Other people have reported other cards. The information on this is just too scarse, as the most populair
card used by members here are ET4000ax cards.

Running boards without cache, I can not give you any advice personally on your board.
I have seen boards on youtube that runs without cache and I know some IBM 486 machines were sold without.
So my advice is to run over the settings for cache, and if there is no specific "no cache installed" setting,
then you might just want to give it a go.

If you have trouble finding an ET4000 ISA card or, they are a bit pricey, then a Cirrus Logic will also do.
I have a CL-GD5424 that performs just as well as my ET4000. They tend to be a bit more reasonably priced.

Agreed with all above, just adding some extra little bits 😀

SRQ wrote:

I have a few questions relating to finishing a project.
Firstly, can you mix and match 30pin ram as long as it's still paired? IE I have 8 slots, if I get 4 4MB sticks can I fill the rest with 1MB sticks?

Yes, but some boards may want larger or smaller modules as the first bank, so sometimes you may need to shuffle a bit.

SRQ wrote:

Secondly, how was old ram compared speedwise? Nanoseconds? Does it make any real difference?

The speed ratings of these modules is the maximum ratings these modules can run at, but if your system is slow enough then it doesn't matter (kinda like a bike and a car are equally fast when going 2km/h).

SRQ wrote:

I can double my 486's cache to 256, will that make any real difference? Doing so would require I strip it from a second 486 board that has a bad bios but I was hoping to repair, would it still work with 0 cache for testing?

It will increase the cacheable area, I don't think it will make a vast difference otherwise?
I think it's more important to at least have more cache then no cache whatsoever.

SRQ wrote:

Finally, two upgrade questions:
Are DX2 processors drop into DX1 systems? This system dates to 1989 (Maybe 1991, hard to tell. Asus ISA-486 board), it's a DX33 system as is. Doesn't have any jumpers for mulitpliers, just a jumper for 24/33 or 50Mhz.

There actually exist drop-in replacements for DX-33, they are called "Overdrive" and made by Intel. You can read a bit about these CPUs over here https://en.wikipedia.org/wiki/Intel_80486_OverDrive
There are also other upgradechips made by(for instance) Kingston.

SRQ wrote:

What's the best ISA video card, and is there any real difference in perfomance? There's no VLB slots on this board, and it currently has an ATi XL24. Is that fast enough that something faster would be limited by the ISA slot?

What the others have said.

If you have VLB or PCI slots, it might be recommendable to use one of those slots for your graphics card, if only because you'll have more options and thus you could opt to use a cheaper solution.

SRQ wrote:

WD made video cards? waaaat

Yes, and they were actually pretty darn good at it.
You might know them by their branding of 'Paradise'.
Paradise SVGA cards were among the best in the late 80s/early 90s.

brostenen wrote:

Running a Dx2-66 in a non-Dx2 system, might make it post. Though you will only run it as an Dx-33.

It will work as DX2-66 as DX2 internally multiplies by 2. Motherboard has nothing to do with it. In any case a 5V cpu should be installed.

Guess I'm just gonna have to get the DX2 and see if it works.
Interestingly I tried switching the jumpers from 33 to 50 on here, the DX33 booted and ran fine... at 33mhz. Was hoping I could overclock 🤣

kixs wrote:

It will work as DX2-66 as DX2 internally multiplies by 2. Motherboard has nothing to do with it. In any case a 5V cpu should be installed.

I think you're right.
I believe the main difference between the 'Overdrive' and the 'regular' DX2-66 is that the Overdrive came with a heatsink glued on, so it was ready to be installed as an upgrade for a passively cooled system (as all 486DX-33 systems were).
The DX2-66 would generally be installed with a clip-on heatsink by the OEM.

So if you go for a non-overdrive, I think it will work, but you probably want to put a heatsink on there to be safe.

I definitely will, there's no clips on this but I'll just paste the thing on, will borrow one from a K6 for it.

also 🤣 the default DX-33 has no heatsink or cooler, at all. I find it hilarious to consider how far we've come cooling wise. It can even do Doom on low graphics!

I still use a passive cooler on my DX33.
It is running hot, and it's old, vintage and I will better be safe than sorry.