Is the PS2 version viable for running this game on competitively? Would it be akin to the Xbox or more like GCN for loads?

Its a CD as opposed to a DVD, meaning only fat ps2s can reliably play it, if that helps.

I'm not as familiar with the PS2 version compared to Xbox and GCN, but I believe PS2 is a bit faster than GCN, but not as fast as Xbox or PC. I also don't know if there are any loading differences between playing on a fat PS2, slim PS2, PS3 or PS4, but I wouldn't be surprised if there were.

I don't think you could beat the WR on PS2 - the Xbox version is ~6min20s faster than GCN and I imagine the difference between Xbox/PS2 isn't too far from that. That being said, you could easily get a sub-1h or even sub-55, there have been many improvements over the years that no one but me have done runs with. =P If you want to run ILs, almost every version is equally good (there are some miniscule differences), since load times don't matter.