I wouldn't think it would matter either way as long as all of the connections (connectors-to-strap, connectors-to-chassis/tranny) are good, and soldered cable-to-connectors would be better than crimped! I would however, if using something like battery-type cable, add a little extra length to it to help compensate for the movement of the engine/tranny while driving. The original type braided ground cable are very flexible which allows them to get away with using shorter ground strap lengths.
All that crap said, I prefer the braided type myself. I'm using an aircraft ground strap I got off Ebay cheap a couple of years back. Similar to original, but about twice the width (read: heavy-duty).
It doesn't say "Porsche" on it, but here's a possible alternative. Ask the seller as to the total length of the strap:
http://cgi.ebay.com/ebaymotors/ws/eBayISAP...&category=34202