Following Dries' suggestion to run some benchmarks comparing Drupal's performance after an upgrade to 4.7 (CVS HEAD), I've gone ahead and collected some results.
I used general purpose testing machine with Apache 2.0.53, PHP 5.0.5, MySQL 5.0.15, and Zend Optimizer 2.5.7. The installation has 50 nodes, and 500 comments generated by devel.module.
The following values are in milliseconds.
Path: / (-9.4%)
min mean[+/-sd] median max
4.6: 200 1142 518.2 981 4176
4.7: 380 1034 208.4 1021 1802
Path: /node/1 (-8.4%)
min mean[+/-sd] median max
4.6: 210 1155 530.5 991 3755
4.7: 220 1058 313.4 1051 2473
Path: /tracker (-3.9%)
min mean[+/-sd] median max
4.6: 200 1084 337.6 1011 2313
4.7: 230 1042 275.8 1031 1922
Path: /admin (+7.7%)
min mean[+/-sd] median max
4.6: 220 1306 638.6 1071 4566
4.7: 210 1419 602.8 1261 4035
Path: /admin/modules (+16.4%)
min mean[+/-sd] median max
4.6: 190 968 244.8 951 1932
4.7: 250 1158 379.0 1071 2493
[edit. I attached the raw logs. sorry, their order is not the best, despite I uploaded them in order. Also, they are from a previous run, smaller amount of content.