Glad to know it's ok to use the 3DS VC version. Some PSN downloads of PS1 games are a bit "off" from the original and not permitted for competition purposes-- WipEout, for example, on the WipEout Zone online community. It'll be much easier for the MK community to grow in the future if the digital versions are fair game

I suppose in some ways the 3DS VC version of MKSC is more "trustworthy" for records etc. than an original cartridge played on a GBA or DS, because the 3DS hasn't been hacked yet

For sure, YMMV with the 1:1 screen mode. I prefer it to the 'upscaled' version because it is sharper and non-distorted. I'm nearsighted and play with the 3DS pretty close to my eyes, so the image size doesn't bother me. The grips help *a lot* with making the d-pad more easily assessed and the whole system more ergonomic-- the position of the game on the top screen is just about perfect, for me, in terms of being in my line-of-sight when holding the system.
I have several cartridges of MKSC that I picked up when the title went Player's Choice some years back in the U.S.-- this has been handy for saving ghost data on all tracks. I never loved the ergonomics of the options I had to play MKSC, though, and am considering using the 3DS version if I get back to setting PRs and stuff.