There could also be issues of copy protection in there too.
I've never had problems with small files and I have an old pc with IDE drives. Nero caches them before the burn. I never needed to go below 8x even when burning 25,000 files on a dvd. If you have a PC of same era as Windows 7, I can't imagine there would be a speed problem that would require going to 4x on dvd-r (unless Windows 7 does not cache). I guess Virus452 could try just in case.