Overclocking is easy enough with v3 firmware on bitmaintech website. The v3 has a pull down menu for speeds. There is an s3 support page somewhere around here and someone will know whats going on if you don't.

If your seeing them on ebay it probably means its time to buy the s3+ through proper channels. I'd just hope if there's a push there them there I'd get a good price if the s3+'s dc controller improves hashing for future overclocking to sell my s3-. S4 can't be that far behind if they can keep prices down.

Just make sure credit card or not that if he charges you make sure you jump him so you don't have a second one unintentionally.