Exclude App from Android 2.1 on Android Market for Performance Reasons?
Are there really some 2.1 phones out there that are very slow, say, using the speed of the Evo as a benchmark?


Yes, absolutely.  I can't play Angry Birds on my HTC Hero running 2.1 because of poor performance.  The game plays fine on my wife's newer Evo.

My advice would be to see if you can buy an old used handset to test your apps on yourself.  That way you'll be able to head off any negative reviews by targeting devices where you know your app performs well.