DDR3 versus GDDR5 when all else is identical?

[Dagget]

To what extent does the memory affect bitcoin performance?

Specifically, I am filling a PCI Express x 16 slot with the best single-width card I can find (double slot cards would crowd the next GPU and cause heating issues)

The following are two cards from the same mfgr, and which only differ in memory type (and $10 in price)

For this type of work, will one memory type or another make a significant difference?

PowerColor AX7750 1GBK3-H Radeon HD 7750 1GB 128-bit DDR3
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131481

PowerColor AX7750 1GBD5-DH Radeon HD 7750 1GB 128-bit GDDR5
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131461

[DeathAndTaxes]

None.  Bitcoin mining uses a negligible amount of GPU memory.