Alright in terms of performance here is how it goes.

3GS has OMAP and a 600mhz processor. The processor is certainly speedy and more than sufficient for almost everyone.

N1 has Snapdragon and a 1ghz processor. Currently the fastest CPU on the market.

The 3GS has a slower processor than the Nexus One it's proven, they are both based off ARM cortex but the Snapdragon pushes the CPU a lot more and the results are a much faster CPU. Here's the catch, 3GS uses OMAP which has a dedicated PowerVR GPU in it, it's much better than the Snapdragons ATI GPU but snapdragon's GPU can still hold it's ground. In the end the 3GS has a much better GPU overall.

Basically, it's a trade off......3GS uses a downclocked version of the Samsung CPU which runs at 800+mhz stock but was put to 600mhz for power reasons and watt per burn or w/e. Basically it's a much better trade off to run it at 600mhz instead of 800mhz. The Snapdragons 1ghz CPU is much faster than the 600mhz 3GS but it's nothing ridiculous where both wouldn't be able to run anything flawlessly. Snapdragon just has faster web page loading times but only by a couple of seconds on some tests and a pretty large 7 sec margin in some. Take note: the 3GS is from June 2009 while the Nexus One is using an updated CPU from January 2010. Apple has already made the A4 chip which is faster than Snapdragon and implemented it in their iPad. The 3GS is better in 3D applications though because it's PowerVR GPU is much better than the Snapdragons integrated ATI. It's basically like a battle of Integrated vs. Dedicated where the 3GS has the dedicated.

In the end, i'd say they are about even, they both are better in different terms.

But to answer your original question:

I have gotten average download speeds on my 3GS of about 1750kbs on AT&T's 3G network in New York. Web browsing on the 3GS is great and speedy now, AT&T has greatly improved their network in NY........the N1 will have faster web browsing times though but it's nothing noticeable or to brag about.

Im going to keep my 3GS until an LTE iPhone comes out or whatever amazing LTE AT&T phone comes out next year. I recommend most of you do that also. Next year is going to be CRAZY!!!! for phone releases. Forget about the N1, Samsung Galaxy S, iPhone 4G........a lot of better phones are going to be here a year from now and with LTE, HD streaming and all that is going to be possible, LTE is going to open the doors for so many more things.