It seems that most chip makers exagerate their claims. One thing they do is raise the rev limit, for example my early Dinan chip goes to 7500 rpm. Is this a good thing? Hard to say, but newer Dinan chips keep the factory 7200 rpm limit...

I wish my rev limit was factory, because at WOT and 7000+ rpm, I'm kinda too busy to be watching the tach rocket up...

On the E34 M5 mailing list, the D'Sylva chip seems to be preferred to the Dinan chip (URL below). In fact, I'll offer to sell you my Dinan chip for $100 and buy myself the D'Sylva chip!

http://groups.yahoo.com/group/bmwe34m5/
http://www.dsylva-tech.ca/