Dual RTX3080 or RTX3090

I've been looking into water cooling them. The GPU used is the short form (not the correct term) but what isn't clear to me is, does the term "reference" cover the short version.

I also have no experience water cooling a GPU. I looked at the EK water blocks but I've yet to research what else is needed, a pump and radiator for certain but probably also a reservoir. In my case all of these will need to be external.

The PSU supplied by DELL is 1k. Even when gaming on max, the R11 only pulls 380-420 watts. Well under the PSU rating. I can see the GPU is pulling nearly half of that so why would you suggest a larger PSU? 

I thought the oem Dell 3090 was 2.5 slots, so everything else aside, I'm not sure you'd physically be able to stick two 3090s in there.  

Of that I was unaware. I won't know until I receive the R12. It would be a bummer if that is true but not a game changer. See what I did there? a little pun for humor.

Keep in mind that Nvidia officially dropped support for SLI/NVLINK with the introduction of the 3000 series cards, on all except for the 3090.  You do need the bridge (around $70) to run them in SLI essentially as one unit to increase performance (as opposed to Physx for example).  But it is essentially a dead-end feature for gaming purposes.  Not really sure how, from a gaming perspective, it would be a worthwhile investment with SLI 3090. 

Bottom line, SLI is essentially dead, and there is no Nvidia support for SLI 3080. 

I think you would have a hard time not bottlenecking an SLI configuration. You would need to invest in a top of the line CPU, memory and motherboard solution. Would become very expensive and unless you have some special case use, total overkill for gaming.

My RTX3080 consumes around 300 Watts at it's maximum performance.

With 2, that would be 600 Watts. That leaves theoretically 400 Watts for everything else.

I do say theoretically, because practically you will have the 1000 watt divided over multiple voltages, like 3.3V, 5V, 12 V etc...

For the RTX series you need 2 x 150 watt from 2 external 12 volt connectors + 75 watt from the PCIe slot.

So 750 Watts just for those, leaving only 250 Watts for everything else. Fans, power for MB, USB power, LED lights, pump for liquid cooler, CPU, memory, chipset etc...

On top of that, a 1000 watt power supply will have limitations on how much power is available per voltage rail. The 12 volt rail might have a maximum of 950 Watts available.

Then you have losses that vary with power supply loads and power supply certification/efficiency, and before you know it a 1000 Watt PSU cannot reliably feed 2 x RTX 3080 or 3090 cards.

For 2 I would get a 1200 Watt power supply with a good certification. and a good efficiency.

Look at it was a car. You want it powerful enough to drive around in day to day without the need to constantly push the engine to it's maximum limits.

The 3090 is 2.5 slots thick.  As others have stated, power might be an issue.  And people seem to have issues with the case itself not keeping things cool even with a single card.  Though I don't understand how that could happen unless they're having component issues or there's some wacky environmental factors happening in whatever room their R11's are in.

But unless you want to climb the dual 3090 3DMark leaderboard, there's no point to SLI with any modern game.

I game but not a lot. Solidworks can use two for rendering to speed things up.

This can't be done with separate computers. 

I am primarily buying the DELL systems because everyone else with stock of the RTX3090 is wearing their <--->hole hat and asking for double the MSRP. Even some are asking for double on used cards that they probably burned the heck out of (or why else would they now be selling the GPU?)

Any boutique with stock of RTX3090 is also wearing the <--->hole hat, charging 5k for something not worth a dime over 3k. They blatantly do this because any 3yr old can do a search and see what the other parts in the build cost. 

Where did you get yours? I looked at the company site and aside from the shipping charge, they are assessing a VAT which seems unusual to me as I do not live in the EU and this isn't being imported into the EU, rather the opposite.