www.segastyle.com somebody already mentioned it earlier in this thread. The guy that runs that site is THE MAN
. If you don't want to deal with messy soldering, get an Action Replay from him and flash it with the Pseudo-Saturn exploit, it will boot everything, imports, backups, homebrew, backups of imports etc. Most Saturn modchips only boot domestic backups but no imports (with the exception of the preflashed bios chips you mentioned. Honestly if all you care about is booting original imports (no backups), your best bet is just an Action Replay (you don't have to hack it) it boots imports right out of the box. Just put the cartridge in your console and don't remove it to avoid damage to the cartridge slot. Get the 4 in 1 like I have as it serves as an extra 4mb RAM cart too.
I just don't see the sense in doing all that soldering when there's a much safer solution, that's super easy to use with the same end result. I mean to each their own, but to me the cartridge method works fine. Of course, I'm using the Pseudo-Saturn setup now so I can boot backups and homebrew too without swapping, which can be a pain to set up initially, but the end result is great and the risk of damaging something setting it up is pretty low, whereas trying to replace the bios can be pretty risky....