Performance has nothing to do with the iPad, it's based on coverage where you end up. I had my iPad (1) with me in (Eastern) Europe this summer and 3G signal strength really depended on where I was (exactly like it dies in the US). Overall, the GSM (AT&T) model makes life much easier if you do any traveling abroad.
No issues while I was in Singapore. There are I think 3 carriers that offer iPad data plans.
1. SingTel
2. M1
3. iCELL
I chose SingTel and while their pricing was a little high, they did offer unlimited 3G data. How long are you going to be there as that makes a difference? There is also an option for free WiFi in many areas of Singapore City. You might need a little local help getting the WiFi password sent to you via SMS.
I used SingTel for the Micro-SIM, $12.60 with 3 days unlimited data and then an additional $10 for 2 more days of service. For me it was not a good value as my hotel package covered free WiFi for multiple devices.
I used mine (ipad 2 3G AT&T 64gb model) in the Philippines for 2 weeks with a Globe prepaid sim card. I had to cut it into a micro sim size and also had to change the apn settings. I used the unlockit website to change the apn settings for the iPad 2. It worked seamlessly .