Yes, no and it all depends...seriously, not trying to be a smarta$$. The amount of compression that's ok is dependent on a lot of variables, eg., main movie vs. complete disc, source (TV, studio disc - how much the original was compressed), viewing monitor/screen, burn, etc., etc. Many ppl. feel down to about 80% is the limit. I've gone to 67-70 % or so with good results, down to 53-55% on some TV series, but this is not a hard and fast rule. If you want more info, just do a search on the forum, this topic has been covered in-depth.
Sorry, I have platinum, never used CSS Free Pro, and Ultra DVD.