Geoff's got a valid point. The vast majority of current Bug owners use some other car as a daily driver. There's no way to rack up the miles if you only use your VW on the weekends or sunny days. My recommendation for you is to get the 94s. You can easily get 30k miles out of 94s. How many years will that get you at your current annual mileage rate? Most guys won't get 30k miles in 10 years, and it will be apart every year anyway to change something.
On the other hand, I know for a fact that I will drive mine for a long time and rack up the miles, so that's why I have 90.5s. There are many that have achieved the magical 100,000 miles with 90.5s, but I've never heard of anyone who's built an engine with 94s then driven it 100k, without taking it apart. some have claimed to have gone 100k with a re-ring job or 2 in between, but that doesn't count. The P&Cs in my 2 liter have about 36-37k miles on them. The engine in my car hasn't been out in 3 years.
Its not just the wall thickness that gives the 90.5s the advantage. The outside diameter of the cooling fins is the same whether you have 94s or stock 83s. The cylinders have to fit into the cooling tin. A 90.5 will have longer fins and more cooling area than 94s. Since 90.5s will theoretically make less power, there's less heat to dissipate.
