I know this is very specific and most people probably haven't even considered running like this, but I have this game set up as a DSiware VC install using 3DS homebrew.

I don't think this should change loadtimes/performance since it uses the same thing that a DS cartridge would and it seems about the same in terms of overall performance.

Would this be on the leaderboard? I have a 2ds XL capture card, so I'd be able to show this off it that's needed in any way while making this decision.

Yeah no it's fine! capture card runs are always better than having someone sending an upside down bad quality video. The loading time in general on the leaderboard is an issue if you want you could compare IGT vs RTA of a run in Grand Prix. Usually there is about 1min5s to 1min15s between RTA and IGT in a GP run.

Aight, thanks!

Am I the only one who plays on a 2DS?

The hardware is the same so it doesn't matter.

(Also, pro tip, don't respond to old forums for no reason.)