I tried resampling a very large, 2 hr long, flac recently with Sound Forge. It was unbearably slow, so I converted it to wave and the process was several times faster. I didn't quantify it, but it seemed more than twice as fast to process.
If your concern is quality, then I think you should take the term 'lossless' at face value. I believe the primary reason that lossless formats are the only ones adopted by this community is that it doesn't matter how many times you you convert between lossless format and wav format, you won't lose any information, providing no data corruption occurs.
I think the guy that thinks his lower compression level flacs sounded better than higher compression level flacs needs to take the pepsi challenge in a controlled environment. I think his opinion was colored by his pre-conceived notion.