Most of the 30 retailers on the Keynote Mobile Commerce Performance Index registered within a few places of where they fell on last week’s index, showing consistent performance by m-commerce web sites.

Walmart.com moved up one to take the top spot. Its m-commerce site home page downloaded on average in 5.86 seconds and it did so successfully 99.30% of the time. It earned a score of 990 out of 1,000, according to mobile and web performance management firm Keynote Systems Inc. Lowe’s Cos. Inc. dropped one spot to second with a score of 988. Its home page downloaded in 6.18 seconds and did so successfully 99.38% of the time.

Brookstone Inc. climbed two spots to No. 3, earning a score of 948. Its download time was 6.40 seconds and its success rate was 99.14%. Walgreen Co. stayed in the No. 4 slot with a score of 913. Its download time was 7.53 seconds and success rate was 99.20%. And Amazon.com Inc. moved up one to No. 5 with a score of 907. Its download time was 6.60 seconds and success rate was 98.91%.

The average score for all retailers on the index was 736. The average m-commerce site home page download time was 9.75 seconds and the average success rate was 98.53%.

Click here and then click on Keynote Mobile Commerce Performance Index Part 1 and Part 2 to see this week’s complete results for all 30 retailers on the index.

Keynote Systems measures 30 representative m-commerce sites exclusively for Internet Retailer. The sites include merchants in various categories and channels, and of various sizes, ranging from such giants as Amazon.com, Sears Holdings Corp. and 1-800-Flowers.com Inc., to midsized retailers like Sunglass Hut, Toolfetch.com LLC and Your Electronic Warehouse. Keynote tests the sites in the index every hour Monday through Friday from 8 a.m. through midnight Eastern time, emulating four different smartphones on four different wireless networks: Apple Inc.’s iPhone 4 on AT&T, the HTC Evo on Sprint, the BlackBerry Curve on T-Mobile and the Droid X on Verizon. The HTC Evo and the Droid X run Google Inc.’s Android operating system.

Keynote combines a site’s load time and success rate, equally weighted, into a single score. Given both performance and availability are important, the score reflects the overall quality of the home page; a higher score indicates better performance. Scores also reflect how close sites are to each other in overall quality. The index average score is the midpoint among all the sites’ scores.