On my '76 2.0 I ran 205-50-15s and had lots of room on BOTH sides. On my '70 I ran 205-50s and had comparatively less room, but still no rubbing.
What brand wheels are you running? Factory wheels with that side tires shouldn't rub at all, but it is dependent on Ride height and alignment.
A 205-55 would be marginally taller.
Have you already rolled your fender lips? (this is a popular way to gain another 1/2" of clearance.
Here's a link to my photobucket site.. should have some pics to help you see better...
Pictures by racer_d911 - Photobucket
http://i528.photobucket.com/albums/dd328/racer_d911/Porsche914pictures006.jpg
http://i528.photobucket.com/albums/dd328/racer_d911/Porsche914pictures004.jpg
In my opinion the 50 series is a bit short on a street car. I used to like running 195-60-15s but for me as they stoped making "R" comps in 60 series, there wasn't really much choice.
Recall that STOCK sizes are closer to 165 width!