Two old mates who've "done a bit" by anybody's standards, both rate the collie x labs they used as kids rabbiting very highly, different bitches, in different decades, so random bred, one's a well known terrier man, and the other lads well known for lurchers, but they both kept Springers for over 30 years, so i know what the collie x labs are being judged against, and they still rate the collie/lab.
i knew a lad back in the early 80s who had 2 collie/lab bitches great markers worked well with ferrets and nets. used to work old railway bankings waste land etc flushed plenty for the lurc